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Sep 15, 2022

Gastrointestinal cancer experts Dr. Aparna Parikh and Dr. Kristin Ciombor discuss the treatment implications of the phase 3 PARADIGM trial and other advances in colorectal cancer with guest host and ASCO Daily News Associate Editor, Dr. Shaalan Beg.



Dr. Shaalan Beg: Hello, and welcome to the ASCO Daily News Podcast. I'm Dr. Shaalan Beg, your guest host of the ASCO Daily News Podcast today. I'm an adjunct associate professor at UT Southwestern's Simmons Comprehensive Center and vice president of Oncology at Science 37. I'm delighted to welcome Dr. Aparna Parikh, and Dr. Kristen Ciombor to the podcast today.

Dr. Parikh is an assistant professor of Medicine at Harvard University and a GI medical oncologist at the Mass General Hospital Cancer Center. Dr. Ciombor is an associate professor of Medicine and GI medical oncologist at the Vanderbilt University Medical Center.

Today, we'll be discussing exciting new approaches using EGFR inhibitors as frontline therapy in colorectal cancer, and promising advances with immune therapy in the treatment of rectal cancer. Our full disclosures are available in the show notes, and disclosures of all guests on the podcast can be found in our transcripts at: Dr. Parikh, and Dr. Ciombor, it's great to have you on the podcast today.

Dr. Aparna Parikh: Thanks so much.

Dr. Kristen Ciombor: Thanks so much for having us.

Dr. Shaalan Beg: We've seen some exciting advances in GI oncology this year. Let's start with colorectal cancer. Dr. Parikh, there have been many trials looking to compare EGFR and VEGF inhibitors in colorectal cancer. We've heard about the IDEA studies, the FIRE trials, and CALGB 80405. At the 2022 ASCO Annual Meeting, we heard the results of the PARADIGM trial. Have we finally answered the question of when to use EGFR inhibitors as frontline therapy for colorectal cancer?

Dr. Aparna Parikh: Thanks so much, Dr. Beg, for this great question. It has been a really exciting year for colorectal cancer across the board. So, the anti-EGFR story is really interesting and has evolved. And maybe just for a little bit of background, we know that colorectal cancer originating from both the right and left side of the colon differ. So, they differ embryologically, and epidemiologically; there are different genetic and molecular aspects to right and left sides of colon cancers. And we have learned over time that in the era of targeted therapy, the primary tumor location has been found to play a very important role, not only in the prognosis of patients but to predict treatment response.

We know that patients that have left-sided colon cancers-- and when we think about left-sided colon cancers, we think about cancers that originate from the splenic flexure and descending colon, sigmoid colon, rectosigmoid junction, and sometimes include the rectum in this as well. The rectals have slightly different molecular features than distal colons.

And we know that these left-sided patients, overall, have better survival benefits than patients that have right-sided CRC. And that includes again, cecum, ascending colon, hepatic flexure, and transverse colon. So, we know that that had prognostic implications, but what about the predictive implications?

And with ASCO, we saw some really exciting data with the PARADIGM study, as Dr. Beg highlighted. We have seen many examples in the past showing the predictive power of anti-EGFR therapy, and anti-EGFR therapy showing a detriment for patients on the right side of the colon. But all these results historically have been obtained by retrospective analysis.

So, retrospective analysis of the pivotal CALGB 80405 study, which is the first-line biologic trial. FIRE-3, which is a similar study, but done out of Europe, and KRYSTAL. So all these studies show the same finding but were all obtained basically by retrospective analysis.

And what we saw with PARADIGM this year, which is exciting to see, is that this was the first prospective trial to test the superiority of an anti-EGFR inhibitor panitumumab versus bevacizumab in combination with standard doublet first-line chemotherapy for patients that were RAS-wild type. I guess I forgot to mention that again, anti-EGFR therapies are only eligible for patients that are RAS-wild type.

We know that RAS-mutant patients and RAS, KRAS HRAS patients don't respond to anti-EGFR therapy. So, the study was looking at RAS-wild type patients, and again, asking the question “was panitumumab better than bevacizumab in combination with chemotherapy for these RAS-wild type patients and for left-sided tumors?”

It was a multicenter trial done in Japan-- and I always commend the Japanese on their work and their designs and ability to do these studies that ask really important questions. And, overall survival was the primary endpoint of the study in patients with left-sided tumors, but they also did a full set analysis including patients that didn't have left-sided tumors.

They had 823 randomized patients. Many patients, a handful did not receive per-protocol treatment, and some were excluded for other reasons relating to inclusion criteria. And they had 400 patients that ultimately received panitumumab and 402 patients that received bevacizumab in the full set analysis. And of those patients, there were 312 and 292 respectively had left-sided tumors. And although the PFS was comparable between the treatment group, we saw that panitumumab in the left-sided patients actually did improve the OS in both patient populations. But when you looked at the left-sided tumors, the difference was 37.9 versus 34.3 months meeting statistical significance.

So, this was an exciting study because it confirmed prospectively what we have seen time and time again, and really behooves us to do early biomarker testing and know RAS status early for these patients with right-sided tumors, as they do derive benefit from anti-EGFR. Maybe I'll just pause there and open it up for more questions or comments from Dr. Ciombor as well.

Dr. Kristen Ciombor: Yeah, Dr. Parikh, I thought these data were encouraging. And as you mentioned, the first prospective data that we have in this setting now that we know this primary tumor sidedness matters. Just on a practical note, what do you do in practice? Do you give a lot of anti-EGFR in the first-line? I find that the toxicity can be challenging sometimes and patients may not want to do that. So, it leaves us in a quandary sometimes.

Dr. Aparna Parikh: Yeah. So, what's interesting and I don't think we have this data clearly answered yet is, I had, especially for kind of a fit patient-- with the previous data that we've seen with TRIBE and others showing a survival benefit with triplet chemotherapy for first-line therapy, my inclination had actually been to prefer triplet-- and we know that triplet and anti-EGFR toxicity-wise is really, really tough to manage, and really no benefit there that we've seen with OS or PFS, even though you maybe do get a little bit of a better response rate with that. And so where I have sort of struggled is triplet versus just doing first-line doublet plus anti-EGFR.

You know, we are not having a discussion about triplet today, but we also saw some data at ASCO showing that perhaps the benefit of the triplet, with the triplet study, is not as much as we had hoped it would've been too. So, it's a good question. I do tend to prefer triplet, I guess, overall, for the healthy, good performance status patient. And then, if not, then doublet. And we, unfortunately, don't have kind of rapid EGFR testing, we're pushing for that. In practice, I think having RAS/RAF status up front would be entirely helpful. It's lumped into our pan-tumor profiling, comprehensive genomic panels. We get microsatellite instability (MSI) status, which I know we'll talk about here next right away.

But I think another reason that oftentimes we don't add it right away, is because we don't have the RAS status right away. So, you just start with a doublet and you may end up sneaking it on later. And then, I'd love to, maybe in another podcast, where we can discuss second-line anti-EGFR therapies and what people do in practice for those right-sided patients should they never get anti-EGFR and later-lines of therapy too. And I would argue, perhaps not, because we do see some patients that do benefit, but it can be challenging sometimes with a fresh new patient to make these decisions. But at least, feel encouraged that we're doing the right thing by adding anti-EGFR therapy if they can tolerate it for the left-sided RAS-wild type patient.

How about you? What do you do?

Dr. Kristen Ciombor: Yeah. Largely, it's a great question. And I don't love giving anti-EGFR therapy. We have an additional issue where I am geographically in that we don't ever give cetuximab because of the high rates of an infusion reaction. So, we pretty much stick to panitumumab and are glad to have that option. But I have started to talk to patients about toxicity and I'm really upfront with the survival data. And it's interesting how people choose differently in terms of what's important to them. And whereas a few extra months in the overall survival may be overshadowed by the toxicity that they have to go through to accomplish that.

So, it's good to have many options though, and that's the important thing, and I think the takeaway, as well.

Dr. Shaalan Beg: So, kind of brings it back to the fundamentals of practicing medicine, right? Bringing our patients and giving them the options that are most available to them. But I'm going to ask both of you one by one: So, if we have our patient with left-sided colorectal cancer, known as KRAS RAS-wild type, do you recommend EGFR therapy and VEGF therapy and allow the patients to decide, or do you feel that we decide if their profile is such that we should continue with VEGF therapy instead?

Dr. Ciombor, do you want to go first?

Dr. Kristen Ciombor: Yeah, I think both are good options. I don't only do bevacizumab in the first-line by any means because we do have that survival data. It mostly comes down to a discussion with the patient in terms of toxicities and survival and how well those balance out.

Dr. Aparna Parikh: Yeah, very similar. I think we have also gotten a little bit more adept at managing toxicity. I'm pretty aggressive about prophylaxis with even doxy and topicals for managing the rash. And so, for some of my younger patients who are wanting to be "aggressive" and want the exposure to anti-EGFR early but are still very mindful of how it's impacting their day-to-day semblance of self, especially for the younger patients, try to be very proactive about side effect management. And then, of course, we have the patients that have the electrolyte wasting and things too that sometimes if it's bad, we are stuck with infusions frequently and you may end up dropping for those patients.

But I think the rash at least I feel like for most patients we can manage if you're aggressive about it too. And I think we have gotten better at that than we were many years ago.

Dr. Kristen Ciombor: Never thought we'd be dermatologists, did we? In training, that was definitely not a path I was good at.

Dr. Shaalan Beg: Dermato-Oncology, rapidly growing field.

So, Dr. Ciombor, the rectal cancer space has evolved very rapidly in recent years, especially when we hear about total neoadjuvant therapy, short-course radiation, watch-and-wait, for those with complete clinical responses. So at ASCO this year, we heard results on immune therapy and rectal cancer. Can you summarize where we are with immune therapy and rectal cancer?

Dr. Kristen Ciombor: So, yes. We heard a lot this year at ASCO; both at ASCO GI and ASCO, from the Memorial group and Dr. Cercek’s group. And this has been a really exciting advance that we're starting to see and potentially paradigm-shifting data. So, we know-- as you mentioned, that our treatment of rectal cancer, specifically, locally advanced rectal cancer has changed a lot in the last few years with a shift to more Total Neoadjuvant Therapy.

And what the Memorial data showed was that for the patients who have microsatellite instability or mismatch repair deficiency, which admittedly, is a small group, but certainly ones that we see in clinic, those patients, on their trial were treated with six months of dostarlimab as neoadjuvant therapy prior to any other treatment; before radiation, surgery, et cetera, and no chemotherapy. And what they found was that actually, six months of dostarlimab in the first 14 evaluable patients actually induced a 100% clinical complete response rate. So, it's really unheard of in most of our trials to see 100%. And I think that caught everyone's attention for sure. I think we have to keep in mind who these patients were and are because they are currently being followed.

So, for instance, these were patients that had pretty bulky node-positive disease, almost all these patients did. These were not really early-stage tumors. We did see that 100% were BRAF-wild type, so it does tell us maybe this is not completely the population that we're all seeing when we do see microsatellite instability since we see a lot of sporadic tumors with BRAF mutations. But on the whole, I mean, these were all MSI-high patients and treated with dostarlimab; the six months, that was the total amount of treatment that they received, though a few patients achieved that clinical complete response earlier at about three months, at the three-month reassessment. And what the clinical complete response rate was, was looking both radiographically, as well as endoscopically, and not seeing any sign of residual tumor.

I think the important thing here is that median follow-up is still pretty short. There are a few patients who are approaching now two years past that dostarlimab therapy and have not had tumor recurrence, but overall, the median follow-up is still quite short. So, I think we do need to continue to follow these patients. We don't have overall survival data yet either. I think we still have a lot to learn, but this is a very encouraging start and certainly, something that could be really treatment-changing for these patients, which again, as Dr. Parikh was saying, we need this molecular profiling early to make treatment decisions right off the bat, not even only for metastatic now, but even for these locally-advanced rectal cancer patients. Because if you think about it, we've all taken care of patients who have to go through chemoradiation, and chemo, and surgery, and have a lot of morbidity from those treatments so that even if you cure them, they're left with a lot of toxicity. So, if we could avoid some of that, even potentially, surgery, that would be wonderful.

But I do caution that this is not the standard of care yet. This is only based on 14 patients with short follow-ups at the current time. But the trial is ongoing, and there are other trials open in this space for patients who don't live in New York or can't get to New York. And for instance, ECOG-ACRIN study 2201 is treating these same patients with nivo and ipi, as opposed to dostarlimab. And that trial is open in about 80 sites now across the US. So hopefully, geographically near all of these patients.

Dr. Shaalan Beg: I think a lot of us and a lot of our listeners, that Monday after the results were announced on ASCO had our phone lines and our patient secure messaging lines blowing up.

Dr. Kristen Ciombor: We should have warned our nurses and our treatment teams that they would be fielding these questions, yes. On one hand, it's wonderful that our data and the science is getting out to patients. But I think we also have to be really careful as to what is reaching them because many of them didn't realize it was for this subset of patient populations. But great that they're asking those questions and wondering-- being advocates for themselves too.

Dr. Shaalan Beg: You use the term clinical complete response. Can you talk about how we determine someone has a complete clinical response and what their follow-up looks like?

Dr. Kristen Ciombor: Yeah. In the context of this study, it was actually, as I mentioned, it was both radiographic complete response, as well as endoscopic. So that's one thing that is a little bit tricky when you think about surveillance of these patients. So, it requires a lot, both in frequent surveillance, MRIs, FLEX SIGs often, digital rectal exams, sometimes doing PET scans or CTs, and patients who-- not only on this kind of study but also in non-operative management; watch-and-wait - really have to commit to very close, very frequent follow-up because if the cancer recurs, we don't want to miss that and lose our chance to cure them. So I think that's a little bit different everywhere, how that watch-and-wait approach really manifests, but I think we're learning how to do that, and working in a multidisciplinary group to make sure that patients get the surveillance that they need.

Dr. Aparna Parikh: Yeah. I totally agree. If we offer, for the MSI-high patients, if we ultimately end up offering neoadjuvant immunotherapy-- and actually, I'm looking forward to your study, Dr. Ciombor, too, I think the monotherapy versus doublet, too, is going to come up for these patients. But I had a patient just a week or two ago that was starting on this approach with neoadjuvant immunotherapy, but for now, as a group, if we're proceeding down that and they do get a clinical complete response, we're deciding to forego even the radiation and surgery. We're following what they did in the OPRA study, which was pretty aggressive surveillance on the backend, both with direct visualization and MRIs, and you're seeing these patients every three months or so.

Dr. Shaalan Beg: Well, thank you Dr. Ciombor and Dr. Parikh for sharing some valuable insights with us on the podcast today.

Dr. Aparna Parikh: Thanks so much for having us. It was a lot of fun.

Dr. Kristen Ciombor: Thanks for having us on.

Dr. Shaalan Beg: And thank you to our listeners for your time today. If you value the insights that you hear on the ASCO Daily News podcast, please take a moment to rate, review and subscribe, wherever you get your podcasts.

Disclaimer: 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.

Follow today’s speakers:

Dr. Kristen Ciombor


Dr. Aparna Parikh



Dr. Shaalan Beg


Listen to additional episodes on advances in GI oncology:

Novel Therapies in GI Oncology at ASCO22

ASCO22: Key Posters on Advances in GI Oncology

Follow ASCO on social media:

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Dr. Shaalan Beg:

Employment: Science 37

Consulting or Advisory Role: Ipsen, Array BioPharma, AstraZeneca/MedImmune, Cancer Commons, Legend Biotech, Foundation Medicine

Research Funding (Inst.): Bristol-Myers Squibb, AstraZeneca/MedImmune, Merck Serono, Five Prime Therapeutics, MedImmune, Genentech, Immunesensor, Tolero Pharmaceuticals

Dr. Kristen Ciombor:

Consulting or Advisory Role: Merck, Pfizer, Lilly, Seagen, Replimune, Personalis

Research Funding (Inst.): Pfizer, Boston Biomedical, MedImmune, Onyx, Bayer, Boehringer Ingelheim, Bristol-Myers Squibb, Merck, Novartis, Incyte, Amgen, Sanofi Recipient, Bristol-Myers Squibb, Array BioPharma, Incyte, Daiichi Sankyo, Nucana, Abbvie, Merck, Pfizer/Calithera, Genentech, Seagen

Travel, Accommodations, Expenses Company: Array

Dr. Aparna Parikh:

Stock and Ownership Interests: C2i genomics

Consulting or Advisory Role: Eli Lilly, Natera, Checkmate Pharmaceuticals, Pfizer, Roche/Genentech, Inivata, Biofidelity, Guardant Health

Research Funding(Inst.): PMV Pharma, Plexxikon, Bristol-Myers Squibb, Genentech, Guardant Health, Array, Eli Lilly, Novartis Pharmaceuticals UK Ltd., PureTech, Mirati Therapeutics, Daiichi Sankyo