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Role of Molecular Classification in Predicting Response to Radiation in Early Endometrial Cancer

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Dr. Shannon Westin and her guest, Dr. Nanda Horeweg and Dr. Carien Creutzberg, discuss the paper "Molecular Classification Predicts Response to Radiotherapy in the Randomized PORTEC-1 and PORTEC-2 Trials for Early-Stage Endometrioid Endometrial Cancer" recently published in the JCO.

TRANSCRIPT

The guest on this podcast episode has no disclosures to declare.

Shannon Westin: Hello everyone, and welcome to another episode of JCO After Hours, the podcast where we get in-depth on manuscripts published in the Journal of Clinical Oncology. I'm your host Shannon Westin, Social Media Editor for the JCO and GYN Oncologist by trade.

And I'm so excited about today's topic because it is a GYN Oncologist dream. Before I start, please note that none of the authors have any conflict of interest. We are going to be discussing molecular classification predicts response to radiotherapy in the randomized PORTEC-1 and PORTEC-2 trials for early-stage endometrioid endometrial cancer. And this was published in the JCO on September 20th, 2023.

And we're going to be speaking to two of the lead authors. First is Nanda Horeweg. She's a senior researcher in the Department of Radiation Oncology at the Leiden University Medical Center in the Netherlands. Welcome.

Nanda Horeweg: Thank you. Happy to be here.

Shannon Westin: And Dr. Carien Creutzberg. She's professor at the Department of Radiation Oncology at the Leiden Medical Center as well.

Carien Creutzberg: Thank you.

Shannon Westin: So, let's get into it. And I want to really level set because we have a mixed audience here. So, why don't you start by speaking about the incidents and mortality of endometrial cancer?

Nanda Horeweg: Yes, of course. Endometrial cancer is the sixth most common cancer in women with around 400,000 new diagnoses made globally each year. And a woman's lifetime risk to get endometrial cancer is around 3%, and the median age, the diagnosis is 61 years.

Most of the women who are diagnosed with endometrial cancer are diagnosed at an early stage, around two thirds, and they have an excellent prognosis. Actually, the five-year survival rates are around 92%. For stage 2 disease, this is actually already going down a bit to 74%. Therefore, stage 3 disease is only 48%. Women that are diagnosed with advanced disease have only a five-year survival, 15%.

Shannon Westin: So, given that we know the majority of endometrial cancers are diagnosed at this early stage, prior to your evaluation, what was known about the optimal way to treat this early-stage patient population?

Carien Creutzberg: Well, of course, the PORTEC trials were done … were started PORTEC-1 in the 19th of the last century, and PORTEC-2 in 2002. So, at that time, there were still many, many women treated adjuvantly with external beam radiation therapy. And we just developed risk factors to decide on their risk and the incidents for radiotherapy.

And in PORTEC-2, because in PORTEC-1 we had seen that most of the recurrences in these early stage cancers were in the vaginal fold, we compared local vaginal brachytherapy only three sessions within full course of pelvic radiotherapy and showed that it had similar pelvic control and survival.

Of course, this study, which Nanda conducted, was a long-term analysis with many new factors known from the translational research in the tissue samples of these patients who participate in PORTEC-1 and 2.

And in the meantime, we've developed much more knowledge on the molecular factors and other important factors such as LVSI, which tell us much more about the individual prognosis to patients. So, the treatment has been developing greatly in the past 20 years.

Shannon Westin: Yeah, and I think this is a great case of less is more, right? We were doing so much for so many people that really didn't need it. And so, really tailoring who needs less treatment, who doesn't need any treatment, and then also, conversely, who may need more treatment that would be missed by the traditional risk factors that you're speaking of.

So, I think that brings us right into my next question, which is just bringing the audience up to date on the cancer genome atlas and how that's changed the way we classify endometrial cancer.

Nanda Horeweg: Yes, I think the molecular classification of the TCGA has shaped the way we think about endometrial cancer, and has huge impact on decisions on adjuvant treatments in the years to come. The TCGA performed an extensive characterization of the endometrial cancers and found that in fact, this disease exists of four different groups.

And the first of the groups I'd like to discuss is the ultra-mutated group, which is characterized by POLE mutations. And this group is shown to have an excellent prognosis in many independent studies. A second group that also has a high mutational burden is characterized by microsatellite instability, and mismatch repair deficiency and has shown to have an intermediate prognosis.

Then there's another group that has a low mutational burden with high copy number alterations and frequent TP53 mutations, and these have a poor prognosis. And then lastly, there's a group that does not have any of the classifying features and is often called non-specific molecular profile or TP53 wild type. And this group also has an intermediate prognosis.

And then finally, there's a small group of cancers that has more than one of these classifying features, the so-called multiple classifiers. And the WHO 2020 has developed an algorithm which can be used to classify them into the four groups.

And that's first on the POLE status. And for the POLE wild type tumors, they are assigned according to mismatch repair deficiency status. And for those that are mismatch repair proficient than POLE wild type, they are classified according to the TP53 status into NSMP or p53 abnormal.

Carien Creutzberg: Yeah, that is because of in the ultra-mutated and hyper mutated groups, many of the other mutations are secondary mutations in the context of the ultra-mutated stage, and they behave like the first molecular group.

Shannon Westin: Yeah. So, that POLE mutation is going to trump anything else, and it's so important. And I will just say as a sidebar, it's been challenging with the price of next gen sequencing sometimes to get that for everyone.

So, sometimes for us when we see a p53 mutation, we actually go back and do the full next gen sequencing to make sure that we're not going to act on that core prognostic feature when it really is in the setting of that more simplistic or that more positive prognostic place.

So, this is great, we already kind of highlighted a little bit PORTEC-1 and 2, but if you don't mind, I would love to get the audience a little bit more information just maybe about the populations that were included as we were figuring out how aggressive to be with radiation just to remind people of that, or to teach them that if they haven't gotten a chance to look at those studies.

Carien Creutzberg: Yeah, that's important to know because PORTEC-1 was still in the era that we also treated intermediate risk stage 1 endometrial cancer patients. So, deep invasion with grade 1 and 2 or superficial invasion with grade 2 and 3. That's what we defined at that point.

Then we compared external beam radiation or no further treatment, showing no survival difference, but a higher risk of recurrence with higher risk being older age over 60, grade 3 for deep myometrial invasion. And we kept those high intermediate risk factors as also similarly found by GOG-99 at the time to do PORTEC-2.

So, at the time, about 50% of patients did not have an indication for adjuvant therapy anymore, and with a high intermediate risk population for PORTEC-2, we compare external beam or vaginal brachytherapy and found the benefit of vaginal brachytherapy. A simple outpatient treatment, very short with almost no side effects ensuring local control.

And nowadays, using the molecular classification of PORTEC-4a, we've compared achieving treatment with or without use of the molecular factors to designated treatment. So, the standard arm is vaginal brachytherapy and investigational arm is first, a molecular risk profile.

And then we give no radiotherapy for those with a favorable profile, then a brachytherapy for the intermediate ones, and for the small group is either extensive LVSI or TP53 mutation or L1 chem overexpression external beam. And we hope to show that less overtreatment and less undertreatment will benefit these patients.

Shannon Westin: Yeah, I'm very much looking forward to the results of PORTEC-4a. But let's circle back and talk a little bit about your amazing work here. So, how did you leverage those patient populations from PORTEC-1 and 2 for the current study?

Nanda Horeweg: Yes. Well, the PORTEC-1 and 2 study provided a unique opportunity to look into differential treatment effects for radiotherapy. And that is because these are randomized trials, so the groups are comparable, and we have long-term follow-up data that's of very high-quality.

In addition, as Carien said earlier, she had the vision already back in the nineties to directly ask the patients permission for the collection of the tissue. So, we have a broader complete biobank for both of these trials, which is quite unique. And our colleagues, Professor Smit and also Charlene Goseff from the pathology department, they have done extensive work on molecular classification, and have molecularly characterized all these cases.

So, this allowed us to include 880 patients in this study, which is the largest so far. And besides like the very good starting point that we have of PORTEC-1 and 2 is that we also chose a design that was optimized to conduct like real causes, the causal effects of the molecular class on radiotherapy response.

So, we tried to preserve this randomization effect, the exchangeability of the groups as much by working with the intention to treat population and not excluding any patients, except for when they did not have the molecular classification assessed.

And also, we looked at areas in the body that were irradiated in one group and not in the other one to really observe the effect of radiotherapy as much as possible. So, looking to the entire pelvis, so local and regional recurrences in PORTEC-1 and looking at pelvic recurrences in PORTEC-2.

Shannon Westin So, how were the intervention outcomes in this study different based on the TCGA classifiers?

Nanda Horeweg: Before I tell you the results of biomolecular group, I think it's good to have the starting point of the analysis here. So, the no hypothesis of my study was to see whether there was any difference, and no hypothesis is that there's no difference. So, if we find a significant effect, then we can actually say that we found something.

And if we start with the POLE group, we did not find any significant difference between the groups allocated to radiotherapy or not. But we did see not a single recurrence in any of the patients that we included from both of these trials.

So, technically speaking, we did not find a predictive effect of the molecular classifier, but a prognostic effect. There's no one's having recurrence, so we can deduct from that, that radiotherapy is probably over treatment.

Then for the MMRd group, we did observe some recurrences, but these were not significantly different between these three groups. So, based on this study, we cannot draw conclusions on which type of radiotherapy we should give to the patients or whether we should give radiotherapy at all.

This was very different for the p53 group. There, the patients had lots of recurrences, unfortunately, as we expected, but we saw a big difference in outcome compared between no radiotherapy at all if it's vaginal brachytherapy where we still had lots of recurrences, and EBRT where we hardly saw any recurrences in the pelvis. And that difference was significantly different.

So, that's an indication that these patients need more than just vaginal brachytherapy, even though it's only stage 1 endometrioid endometrial cancer.

And then in the last group, the NSMPs, we saw even a different pattern where patients who had had external beam radiotherapy or vaginal brachytherapy, both had an excellent local regional control, and the ones that did not receive any treatments had more recurrences. And this was also very significant.

So, there, you would conclude that both therapies are appropriate, but of course, the toxicity profile for vaginal brachytherapy is much more favorable than that of EBRT.

Shannon Westin: We really are getting kind of consistent data around p53 needing more treatment. And I think the natural question that comes here, for me at least, and I know we can't answer it with the work, is would chemo be — would that be that extra treatment, when we saw with PORTEC-3 that the group needed the chemotherapy the most.

So, I think we'll have to continue to work through that and determine is any more treatment what we need or specific treatments really the best. So, this is so intriguing and it's nice that it's consistent, that we're seeing that across these different studies that really kind of lends strength and validity, I think to what we're finding.

So, one of the actions that we're kind of moving towards and that you advocate certainly in your paper is omitting therapy for patients with POLE mutations. Are there any ongoing studies around that that will help us confirm that this is safe for our patients?

Nanda Horeweg: Yeah, that's a very good point. I think the evidence is strong enough now to conduct prospective trials. And of course, these are ongoing, the PORTEC-4a trial was already briefly mentioned there. The patients with poor mutations will be randomized between observation and vaginal brachytherapy. So, that will give us a good indication whether in this high intermediate risk early-stage group omission is safe.

And in addition to that, we are also conducting with the RAINBO Consortium, the RAINBO-BLUE trial, wherein patients also with high-risk features, so non-endometrioid isotypes, LVSI and higher stages are included. And also in those patients, we investigate whether the de-escalation of treatment is safe.

So, we're definitely looking forward to those results to be able to transfer this knowledge to clinical practice later on.

Carien Creutzberg: And maybe it's nice to add that RAINBO BLUE is connected to the Canadian Taper trial. Taper being a general de-escalation trial where the POLE patients in that trial are also feeding into the RAINBO-BLUE. And I know that in North America, many centers will participate in the Taper trial.

Shannon Westin: Yes, I think everyone is very excited and I think it'll be nice to have these two very strong studies that will help us really confirm that that is 100% a test that needs to be done, cost are not — and that will help avoid overtreatment of patients.

So, in line of that, have you all experienced any challenges with implementing molecular testing across patients with endometrial cancer? Any thoughts on how we could potentially simplify? You talked about the rational promise algorithm, which I think is excellent, but I'm just curious to hear your thoughts on this.

Nanda Horeweg: The implementation of the molecular classification can be challenging. We have to be honest about that. And usually, it's the assessment of the POLE status that's causing the problems because that's usually done with NGS, which is quite expensive. It requires a lot of knowledge in the laboratory and it's also a bit time-consuming.

So, that is the bottleneck for most laboratories and for most settings. But this is already changing in a couple of places, like in the UK and the Netherlands, it's being reimbursed by healthcare insurances, and also, in many tertiary care centers in other countries, they're already systematically performing this test.

But of course, there will always be places where this is not feasible. And luckily, there are also cheaper alternatives coming up and are already available at the moment. So, one of them is, for example, standard sequencing, which is not so expensive, but a bit labor intensive.

Some colleagues we work with from India have implemented that in their clinical practice and are perfectly able to molecularly classify the endometrial cancers in daily practice.

Another alternative is a test that we've developed in Leiden that's called the QPOLE test, which is based on qPCR, so that's a technology which we use for our COVID test around the world, so that can be done almost anywhere. And with that, you have a very high accuracy to detect unknown pathogenic variants.

And this is also published in JCO Global Oncology, and can be implemented in any center after a local validation step. And even like more companies nowadays are realizing that this is important. So, I think commercial tests are already becoming available and very more on the market soon. So, I am really hoping that it'll be more available to endometrial cancer patients.

Carien Creutzberg: And they'll offer them at a very low cost and also a rapid turnaround because NGS can take like 10 days. But realizing on a more national level, if you have found one patient with a POLE mutation, the omission of cycles of chemotherapy with all of the patient care around in the hospital is worth much more than just a few POLE tests.

So, we have to look at this and that's I think why our healthcare reimbursement came through that if you look at a population level, it is cheaper, and we'll do an extensive cost analysis in PORTEC-4 just to show this.

Shannon Westin: That is such a good point. I love that and all of the downstream issues that happen potentially with radiotherapy or with chemotherapy, that's really brilliant. And I'm going to take that back, I love these podcasts. I always learn stuff that I immediately start to use.

So, I guess then the last question is, what's next for this particular research and how might we validate what you found?

Nanda Horeweg: Yes. Well, as mentioned earlier, for POLE, we have already put the next step in place. So, PORTEC-4a has completed accrual almost two years ago, and we're very much looking forward to do the final analysis within one to one and a half years.

So, that will be one of the important next step. And of course, the POLE-BLUE trial is open at the moment, and within a couple of years, we also hope to learn more about this group. So, that's very exciting.

Then for the mismatch repair deficient group, while we did not find any particular sensitivity for radiotherapy, and I also don't think that we will conduct another large randomized radiotherapy trial in this group — I think the results that we've observed in the metastasized setting, were really impressive results with immunotherapy are the way forward for this molecular class.

And I think the next thing we should do now is prove whether this works or not in the adjuvant setting. And if that's starting with the high-risk patients, which is something we are currently doing in the MMRd-GREEN trial, which is ongoing in the Netherlands, and soon, will open internationally. And from there on, we can work forward if we see that also in this setting the immunotherapy works well.

Shannon Westin: And I think GY020 also — NCI trial is also looking at the addition of immunotherapy to radiotherapy in that irony at risk.

Carien Creutzberg: Absolutely.

Nanda Horeweg: Yeah. And the KEYNOTE-B21 as well — oh, well, already complete accrue.

Shannon Westin: The B21, yeah. So, I think those are good. Yeah, that's a really good point for that MMRd group that the immunotherapy really is the way to go, and then more work to be done with the no specific molecular profile.

Nanda Horeweg: The NSMP, I think like for the early-stage group, it's quite clear that vaginal brachytherapy is a therapy of choice. But you can of course, try to identify those at such a low risk that you could deescalate treatment. And that's of course what's being done in the Taper trial and also in part, investigated in the PORTEC-4a trial.

Carien Creutzberg: And those with higher risk NSMP that we are revisiting hormonal treatments because 90% are estrogen receptor positive, and they have a clearly better prognosis than those with estrogen receptor negative tumors.

So, those with estrogen receptor positive tumors can in RAINBO-ORANGE, which will be run led by the UK group, see if we can improve quality of life with less intensive adjuvant treatment. And then you came to the p53 group, that's a good one to stop with.

Nanda Horeweg: Yeah, we have very good indications that radiotherapy and chemotherapy is working well for this group. And this is also in line with the guidelines that have been issued in the last few years by many societies. So, I don't think we should change this base of the treatment consisting of radiotherapy and chemotherapy.

But since the prognosis is still rather poor, we need to add systemic agents to reduce the risk of metastasis. And preferably, this should be like well-designed based on a proper biological underpinning, plus something that's not too toxic since we're combining the three therapies together.

So, this is what we try to do in the RAINBO-RED trial where we will investigate the addition of a PARP inhibitor to chemoradiation in the p53 group.

Shannon Westin: Oh, I love that. That's been my whole career, is adding PARP inhibitors wherever I can.

Carien Creutzberg): We might also want to mention the HER2 inhibitors, which are also in about 20% of the p53 group has HER2 overexpression. And there is a trial being set up in NCI with trastuzumab and pertuzumab.

Shannon Westin: My only concern with that one is I think that the antibody drug conjugates are so much more powerful, the TDX data that we just saw from DESTINY is so impressive. And so, I do wonder, like if we need to move on from kind of some of the older HER2, and get with the program and use some of these more powerful drugs.

But with that, I just want to thank Dr. Creutzberg and Horeweg. This was such a great discussion, and obviously, near and dear to my heart talking about endometrial cancer, but I hope our audience enjoyed as well.

Just as a reminder, this was a discussion on molecular classification predicts response to radiotherapy in the randomized PORTEC-1 and PORTEC-2 trials for early stage endometroid endometrial cancer, published in the JCO on 9.20.23.

I am your host, Shannon Westin, and I hope you'll check out more JCO After Hours wherever you get your podcasts. Have an awesome day.

The purpose of this podcast is to educate and to inform. This is not a substitute for professional medical care, and is not intended for use in the diagnosis or treatment of individual conditions. Guests on this podcast express their own opinions, experience, and conclusions.

Guest statements on the podcast do not express the opinions of ASCO. The mention of any product, service, organization, activity, or therapy should not be construed as an ASCO endorsement.

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Innhold levert av Journals Online Team and American Society of Clinical Oncology (ASCO). Alt podcastinnhold, inkludert episoder, grafikk og podcastbeskrivelser, lastes opp og leveres direkte av Journals Online Team and American Society of Clinical Oncology (ASCO) eller deres podcastplattformpartner. Hvis du tror at noen bruker det opphavsrettsbeskyttede verket ditt uten din tillatelse, kan du følge prosessen skissert her https://no.player.fm/legal.

Dr. Shannon Westin and her guest, Dr. Nanda Horeweg and Dr. Carien Creutzberg, discuss the paper "Molecular Classification Predicts Response to Radiotherapy in the Randomized PORTEC-1 and PORTEC-2 Trials for Early-Stage Endometrioid Endometrial Cancer" recently published in the JCO.

TRANSCRIPT

The guest on this podcast episode has no disclosures to declare.

Shannon Westin: Hello everyone, and welcome to another episode of JCO After Hours, the podcast where we get in-depth on manuscripts published in the Journal of Clinical Oncology. I'm your host Shannon Westin, Social Media Editor for the JCO and GYN Oncologist by trade.

And I'm so excited about today's topic because it is a GYN Oncologist dream. Before I start, please note that none of the authors have any conflict of interest. We are going to be discussing molecular classification predicts response to radiotherapy in the randomized PORTEC-1 and PORTEC-2 trials for early-stage endometrioid endometrial cancer. And this was published in the JCO on September 20th, 2023.

And we're going to be speaking to two of the lead authors. First is Nanda Horeweg. She's a senior researcher in the Department of Radiation Oncology at the Leiden University Medical Center in the Netherlands. Welcome.

Nanda Horeweg: Thank you. Happy to be here.

Shannon Westin: And Dr. Carien Creutzberg. She's professor at the Department of Radiation Oncology at the Leiden Medical Center as well.

Carien Creutzberg: Thank you.

Shannon Westin: So, let's get into it. And I want to really level set because we have a mixed audience here. So, why don't you start by speaking about the incidents and mortality of endometrial cancer?

Nanda Horeweg: Yes, of course. Endometrial cancer is the sixth most common cancer in women with around 400,000 new diagnoses made globally each year. And a woman's lifetime risk to get endometrial cancer is around 3%, and the median age, the diagnosis is 61 years.

Most of the women who are diagnosed with endometrial cancer are diagnosed at an early stage, around two thirds, and they have an excellent prognosis. Actually, the five-year survival rates are around 92%. For stage 2 disease, this is actually already going down a bit to 74%. Therefore, stage 3 disease is only 48%. Women that are diagnosed with advanced disease have only a five-year survival, 15%.

Shannon Westin: So, given that we know the majority of endometrial cancers are diagnosed at this early stage, prior to your evaluation, what was known about the optimal way to treat this early-stage patient population?

Carien Creutzberg: Well, of course, the PORTEC trials were done … were started PORTEC-1 in the 19th of the last century, and PORTEC-2 in 2002. So, at that time, there were still many, many women treated adjuvantly with external beam radiation therapy. And we just developed risk factors to decide on their risk and the incidents for radiotherapy.

And in PORTEC-2, because in PORTEC-1 we had seen that most of the recurrences in these early stage cancers were in the vaginal fold, we compared local vaginal brachytherapy only three sessions within full course of pelvic radiotherapy and showed that it had similar pelvic control and survival.

Of course, this study, which Nanda conducted, was a long-term analysis with many new factors known from the translational research in the tissue samples of these patients who participate in PORTEC-1 and 2.

And in the meantime, we've developed much more knowledge on the molecular factors and other important factors such as LVSI, which tell us much more about the individual prognosis to patients. So, the treatment has been developing greatly in the past 20 years.

Shannon Westin: Yeah, and I think this is a great case of less is more, right? We were doing so much for so many people that really didn't need it. And so, really tailoring who needs less treatment, who doesn't need any treatment, and then also, conversely, who may need more treatment that would be missed by the traditional risk factors that you're speaking of.

So, I think that brings us right into my next question, which is just bringing the audience up to date on the cancer genome atlas and how that's changed the way we classify endometrial cancer.

Nanda Horeweg: Yes, I think the molecular classification of the TCGA has shaped the way we think about endometrial cancer, and has huge impact on decisions on adjuvant treatments in the years to come. The TCGA performed an extensive characterization of the endometrial cancers and found that in fact, this disease exists of four different groups.

And the first of the groups I'd like to discuss is the ultra-mutated group, which is characterized by POLE mutations. And this group is shown to have an excellent prognosis in many independent studies. A second group that also has a high mutational burden is characterized by microsatellite instability, and mismatch repair deficiency and has shown to have an intermediate prognosis.

Then there's another group that has a low mutational burden with high copy number alterations and frequent TP53 mutations, and these have a poor prognosis. And then lastly, there's a group that does not have any of the classifying features and is often called non-specific molecular profile or TP53 wild type. And this group also has an intermediate prognosis.

And then finally, there's a small group of cancers that has more than one of these classifying features, the so-called multiple classifiers. And the WHO 2020 has developed an algorithm which can be used to classify them into the four groups.

And that's first on the POLE status. And for the POLE wild type tumors, they are assigned according to mismatch repair deficiency status. And for those that are mismatch repair proficient than POLE wild type, they are classified according to the TP53 status into NSMP or p53 abnormal.

Carien Creutzberg: Yeah, that is because of in the ultra-mutated and hyper mutated groups, many of the other mutations are secondary mutations in the context of the ultra-mutated stage, and they behave like the first molecular group.

Shannon Westin: Yeah. So, that POLE mutation is going to trump anything else, and it's so important. And I will just say as a sidebar, it's been challenging with the price of next gen sequencing sometimes to get that for everyone.

So, sometimes for us when we see a p53 mutation, we actually go back and do the full next gen sequencing to make sure that we're not going to act on that core prognostic feature when it really is in the setting of that more simplistic or that more positive prognostic place.

So, this is great, we already kind of highlighted a little bit PORTEC-1 and 2, but if you don't mind, I would love to get the audience a little bit more information just maybe about the populations that were included as we were figuring out how aggressive to be with radiation just to remind people of that, or to teach them that if they haven't gotten a chance to look at those studies.

Carien Creutzberg: Yeah, that's important to know because PORTEC-1 was still in the era that we also treated intermediate risk stage 1 endometrial cancer patients. So, deep invasion with grade 1 and 2 or superficial invasion with grade 2 and 3. That's what we defined at that point.

Then we compared external beam radiation or no further treatment, showing no survival difference, but a higher risk of recurrence with higher risk being older age over 60, grade 3 for deep myometrial invasion. And we kept those high intermediate risk factors as also similarly found by GOG-99 at the time to do PORTEC-2.

So, at the time, about 50% of patients did not have an indication for adjuvant therapy anymore, and with a high intermediate risk population for PORTEC-2, we compare external beam or vaginal brachytherapy and found the benefit of vaginal brachytherapy. A simple outpatient treatment, very short with almost no side effects ensuring local control.

And nowadays, using the molecular classification of PORTEC-4a, we've compared achieving treatment with or without use of the molecular factors to designated treatment. So, the standard arm is vaginal brachytherapy and investigational arm is first, a molecular risk profile.

And then we give no radiotherapy for those with a favorable profile, then a brachytherapy for the intermediate ones, and for the small group is either extensive LVSI or TP53 mutation or L1 chem overexpression external beam. And we hope to show that less overtreatment and less undertreatment will benefit these patients.

Shannon Westin: Yeah, I'm very much looking forward to the results of PORTEC-4a. But let's circle back and talk a little bit about your amazing work here. So, how did you leverage those patient populations from PORTEC-1 and 2 for the current study?

Nanda Horeweg: Yes. Well, the PORTEC-1 and 2 study provided a unique opportunity to look into differential treatment effects for radiotherapy. And that is because these are randomized trials, so the groups are comparable, and we have long-term follow-up data that's of very high-quality.

In addition, as Carien said earlier, she had the vision already back in the nineties to directly ask the patients permission for the collection of the tissue. So, we have a broader complete biobank for both of these trials, which is quite unique. And our colleagues, Professor Smit and also Charlene Goseff from the pathology department, they have done extensive work on molecular classification, and have molecularly characterized all these cases.

So, this allowed us to include 880 patients in this study, which is the largest so far. And besides like the very good starting point that we have of PORTEC-1 and 2 is that we also chose a design that was optimized to conduct like real causes, the causal effects of the molecular class on radiotherapy response.

So, we tried to preserve this randomization effect, the exchangeability of the groups as much by working with the intention to treat population and not excluding any patients, except for when they did not have the molecular classification assessed.

And also, we looked at areas in the body that were irradiated in one group and not in the other one to really observe the effect of radiotherapy as much as possible. So, looking to the entire pelvis, so local and regional recurrences in PORTEC-1 and looking at pelvic recurrences in PORTEC-2.

Shannon Westin So, how were the intervention outcomes in this study different based on the TCGA classifiers?

Nanda Horeweg: Before I tell you the results of biomolecular group, I think it's good to have the starting point of the analysis here. So, the no hypothesis of my study was to see whether there was any difference, and no hypothesis is that there's no difference. So, if we find a significant effect, then we can actually say that we found something.

And if we start with the POLE group, we did not find any significant difference between the groups allocated to radiotherapy or not. But we did see not a single recurrence in any of the patients that we included from both of these trials.

So, technically speaking, we did not find a predictive effect of the molecular classifier, but a prognostic effect. There's no one's having recurrence, so we can deduct from that, that radiotherapy is probably over treatment.

Then for the MMRd group, we did observe some recurrences, but these were not significantly different between these three groups. So, based on this study, we cannot draw conclusions on which type of radiotherapy we should give to the patients or whether we should give radiotherapy at all.

This was very different for the p53 group. There, the patients had lots of recurrences, unfortunately, as we expected, but we saw a big difference in outcome compared between no radiotherapy at all if it's vaginal brachytherapy where we still had lots of recurrences, and EBRT where we hardly saw any recurrences in the pelvis. And that difference was significantly different.

So, that's an indication that these patients need more than just vaginal brachytherapy, even though it's only stage 1 endometrioid endometrial cancer.

And then in the last group, the NSMPs, we saw even a different pattern where patients who had had external beam radiotherapy or vaginal brachytherapy, both had an excellent local regional control, and the ones that did not receive any treatments had more recurrences. And this was also very significant.

So, there, you would conclude that both therapies are appropriate, but of course, the toxicity profile for vaginal brachytherapy is much more favorable than that of EBRT.

Shannon Westin: We really are getting kind of consistent data around p53 needing more treatment. And I think the natural question that comes here, for me at least, and I know we can't answer it with the work, is would chemo be — would that be that extra treatment, when we saw with PORTEC-3 that the group needed the chemotherapy the most.

So, I think we'll have to continue to work through that and determine is any more treatment what we need or specific treatments really the best. So, this is so intriguing and it's nice that it's consistent, that we're seeing that across these different studies that really kind of lends strength and validity, I think to what we're finding.

So, one of the actions that we're kind of moving towards and that you advocate certainly in your paper is omitting therapy for patients with POLE mutations. Are there any ongoing studies around that that will help us confirm that this is safe for our patients?

Nanda Horeweg: Yeah, that's a very good point. I think the evidence is strong enough now to conduct prospective trials. And of course, these are ongoing, the PORTEC-4a trial was already briefly mentioned there. The patients with poor mutations will be randomized between observation and vaginal brachytherapy. So, that will give us a good indication whether in this high intermediate risk early-stage group omission is safe.

And in addition to that, we are also conducting with the RAINBO Consortium, the RAINBO-BLUE trial, wherein patients also with high-risk features, so non-endometrioid isotypes, LVSI and higher stages are included. And also in those patients, we investigate whether the de-escalation of treatment is safe.

So, we're definitely looking forward to those results to be able to transfer this knowledge to clinical practice later on.

Carien Creutzberg: And maybe it's nice to add that RAINBO BLUE is connected to the Canadian Taper trial. Taper being a general de-escalation trial where the POLE patients in that trial are also feeding into the RAINBO-BLUE. And I know that in North America, many centers will participate in the Taper trial.

Shannon Westin: Yes, I think everyone is very excited and I think it'll be nice to have these two very strong studies that will help us really confirm that that is 100% a test that needs to be done, cost are not — and that will help avoid overtreatment of patients.

So, in line of that, have you all experienced any challenges with implementing molecular testing across patients with endometrial cancer? Any thoughts on how we could potentially simplify? You talked about the rational promise algorithm, which I think is excellent, but I'm just curious to hear your thoughts on this.

Nanda Horeweg: The implementation of the molecular classification can be challenging. We have to be honest about that. And usually, it's the assessment of the POLE status that's causing the problems because that's usually done with NGS, which is quite expensive. It requires a lot of knowledge in the laboratory and it's also a bit time-consuming.

So, that is the bottleneck for most laboratories and for most settings. But this is already changing in a couple of places, like in the UK and the Netherlands, it's being reimbursed by healthcare insurances, and also, in many tertiary care centers in other countries, they're already systematically performing this test.

But of course, there will always be places where this is not feasible. And luckily, there are also cheaper alternatives coming up and are already available at the moment. So, one of them is, for example, standard sequencing, which is not so expensive, but a bit labor intensive.

Some colleagues we work with from India have implemented that in their clinical practice and are perfectly able to molecularly classify the endometrial cancers in daily practice.

Another alternative is a test that we've developed in Leiden that's called the QPOLE test, which is based on qPCR, so that's a technology which we use for our COVID test around the world, so that can be done almost anywhere. And with that, you have a very high accuracy to detect unknown pathogenic variants.

And this is also published in JCO Global Oncology, and can be implemented in any center after a local validation step. And even like more companies nowadays are realizing that this is important. So, I think commercial tests are already becoming available and very more on the market soon. So, I am really hoping that it'll be more available to endometrial cancer patients.

Carien Creutzberg: And they'll offer them at a very low cost and also a rapid turnaround because NGS can take like 10 days. But realizing on a more national level, if you have found one patient with a POLE mutation, the omission of cycles of chemotherapy with all of the patient care around in the hospital is worth much more than just a few POLE tests.

So, we have to look at this and that's I think why our healthcare reimbursement came through that if you look at a population level, it is cheaper, and we'll do an extensive cost analysis in PORTEC-4 just to show this.

Shannon Westin: That is such a good point. I love that and all of the downstream issues that happen potentially with radiotherapy or with chemotherapy, that's really brilliant. And I'm going to take that back, I love these podcasts. I always learn stuff that I immediately start to use.

So, I guess then the last question is, what's next for this particular research and how might we validate what you found?

Nanda Horeweg: Yes. Well, as mentioned earlier, for POLE, we have already put the next step in place. So, PORTEC-4a has completed accrual almost two years ago, and we're very much looking forward to do the final analysis within one to one and a half years.

So, that will be one of the important next step. And of course, the POLE-BLUE trial is open at the moment, and within a couple of years, we also hope to learn more about this group. So, that's very exciting.

Then for the mismatch repair deficient group, while we did not find any particular sensitivity for radiotherapy, and I also don't think that we will conduct another large randomized radiotherapy trial in this group — I think the results that we've observed in the metastasized setting, were really impressive results with immunotherapy are the way forward for this molecular class.

And I think the next thing we should do now is prove whether this works or not in the adjuvant setting. And if that's starting with the high-risk patients, which is something we are currently doing in the MMRd-GREEN trial, which is ongoing in the Netherlands, and soon, will open internationally. And from there on, we can work forward if we see that also in this setting the immunotherapy works well.

Shannon Westin: And I think GY020 also — NCI trial is also looking at the addition of immunotherapy to radiotherapy in that irony at risk.

Carien Creutzberg: Absolutely.

Nanda Horeweg: Yeah. And the KEYNOTE-B21 as well — oh, well, already complete accrue.

Shannon Westin: The B21, yeah. So, I think those are good. Yeah, that's a really good point for that MMRd group that the immunotherapy really is the way to go, and then more work to be done with the no specific molecular profile.

Nanda Horeweg: The NSMP, I think like for the early-stage group, it's quite clear that vaginal brachytherapy is a therapy of choice. But you can of course, try to identify those at such a low risk that you could deescalate treatment. And that's of course what's being done in the Taper trial and also in part, investigated in the PORTEC-4a trial.

Carien Creutzberg: And those with higher risk NSMP that we are revisiting hormonal treatments because 90% are estrogen receptor positive, and they have a clearly better prognosis than those with estrogen receptor negative tumors.

So, those with estrogen receptor positive tumors can in RAINBO-ORANGE, which will be run led by the UK group, see if we can improve quality of life with less intensive adjuvant treatment. And then you came to the p53 group, that's a good one to stop with.

Nanda Horeweg: Yeah, we have very good indications that radiotherapy and chemotherapy is working well for this group. And this is also in line with the guidelines that have been issued in the last few years by many societies. So, I don't think we should change this base of the treatment consisting of radiotherapy and chemotherapy.

But since the prognosis is still rather poor, we need to add systemic agents to reduce the risk of metastasis. And preferably, this should be like well-designed based on a proper biological underpinning, plus something that's not too toxic since we're combining the three therapies together.

So, this is what we try to do in the RAINBO-RED trial where we will investigate the addition of a PARP inhibitor to chemoradiation in the p53 group.

Shannon Westin: Oh, I love that. That's been my whole career, is adding PARP inhibitors wherever I can.

Carien Creutzberg): We might also want to mention the HER2 inhibitors, which are also in about 20% of the p53 group has HER2 overexpression. And there is a trial being set up in NCI with trastuzumab and pertuzumab.

Shannon Westin: My only concern with that one is I think that the antibody drug conjugates are so much more powerful, the TDX data that we just saw from DESTINY is so impressive. And so, I do wonder, like if we need to move on from kind of some of the older HER2, and get with the program and use some of these more powerful drugs.

But with that, I just want to thank Dr. Creutzberg and Horeweg. This was such a great discussion, and obviously, near and dear to my heart talking about endometrial cancer, but I hope our audience enjoyed as well.

Just as a reminder, this was a discussion on molecular classification predicts response to radiotherapy in the randomized PORTEC-1 and PORTEC-2 trials for early stage endometroid endometrial cancer, published in the JCO on 9.20.23.

I am your host, Shannon Westin, and I hope you'll check out more JCO After Hours wherever you get your podcasts. Have an awesome day.

The purpose of this podcast is to educate and to inform. This is not a substitute for professional medical care, and is not intended for use in the diagnosis or treatment of individual conditions. Guests on this podcast express their own opinions, experience, and conclusions.

Guest statements on the podcast do not express the opinions of ASCO. The mention of any product, service, organization, activity, or therapy should not be construed as an ASCO endorsement.

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