JCO PO author Dr. Jun Gong shares insights into his JCO PO articles, “Phase II Study of Erdafitinib in Patients with Tumors with FGFR Amplifications: Results from the NCI-MATCH ECOG-ACRIN Trial (EAY131) Sub-protocol K1" and “Phase II Study of Erdafitinib in Patients with Tumors with FGFR Mutations or Fusions: Results from the NCI-MATCH ECOG-ACRIN Trial (EAY131) Sub-protocol K2”. Host Dr. Rafeh Naqash and Dr. Gong discuss the limited activity of FGFR inhibition in solid tumors with FGFR amplifications and mutations or fusions in this NCI-MATCH phase II trial.

TRANSCRIPT

Dr. Rafeh Naqash: Hello and welcome to JCO Precision Oncology Conversations, where we bring you engaging conversations of clinically relevant and highly significant JCO PO articles. I'm your host, Dr. Rafeh Naqash, Social Media Editor for JCO Precision Oncology and Assistant Professor at the Stevenson Cancer Center at the University of Oklahoma.

Today, we are excited to be joined by Dr. Jun Gong, Associate Professor in the Division of Medical Oncology at Cedars-Sinai Medical Center and lead author of the JCO Precision Oncology article entitled "Phase II Study of Erdafitinib in Patients with Tumors Harboring FGFR Amplifications: Results from the NCI-MATCH ECOG-ACRIN Trial EAY131 Subprotocol K1" and "Phase II Study of Erdafitinib in Patients with Tumors with FGFR Mutations or Fusions: Results from the NCI-MATCH ECOG-ACRIN Trial EAY131 Subprotocol K2."

Our guest's disclosures will be linked in the transcript.

Dr. Gong, welcome to our podcast and thank you for joining us.

Dr. Jun Gong: Thank you, Dr. Naqash and JCO Precision Oncology for having me.

Dr. Rafeh Naqash: We are excited to be discussing some interesting aspects that you have led and published on from the NCI-MATCH trial. We were trying to understand from a background perspective, since this master protocol has been going on for quite some time, could you give us a little bit of background for the sake of our listeners on what the NCI-MATCH is and what were the specific objectives for these two subprotocols?

Dr. Jun Gong: Yes, of course, Dr. Naqash. So, as you may all know, the importance of targeted therapies in the current era of precision oncology. And on that backdrop, the NCI-MATCH was a national multicenter study designed essentially to look for signals of efficacy across various solid tumor and hematologic malignancy types, with a focus on specific mutations. The master protocol is unique in that there are several arms to the trial, each targeting a specific potential targetable alteration using available agents in cancer today.

Dr. Rafeh Naqash: Excellent. Thank you for that background. I know this master protocol has been going on for quite some time with different subprotocols. I believe some of them are immunotherapy-based. Also, you've led two important subprotocols, which are the FGFR amplification and the FGFR mutation or fusion. There are some differences, from what I gather, in responses for the fusions versus the amplifications or mutations versus the amplifications. Could you first delve into the first paper of the fusions, and describe what were the tumor types? As you mentioned in the paper, some tumors were excluded. What was the reason for the exclusion of some of those tumor types? Why did you want to study the fusions and mutations versus the amplifications separately? What was the background for that? Could you highlight some of those points for us?

Dr. Jun Gong: Firstly, as a kind of a more background, FGFR has been a recognizable target for a couple of tumor types. And if you look at the broad landscape of FGFR alterations, they occur in about 5%-10% of cancers, with the majority being FGFR amplifications actually, and mutations and rearrangements following second and third respectively in most commonly identified alterations. With that being said, FGFR mutations and rearrangements have already been established in a couple of tumor types. Actually, the first FDA approval for an oral FGFR inhibitor was erdafitinib, which was the agent used in both of these back-to-back trials. However, erdafitinib was first approved in urothelial carcinoma, and since then, there has been an explosion in oral FGFR inhibitors targeting fusions and mutations in other cancer types, such as cholangiocarcinoma.

More recently, there was even an FDA approval in a myeloid malignancy as well. So, we used erdafitinib, being that it was the first FDA-approved, orally available agent to target this alteration. We conducted the two back-to-back studies in recognition that although rearrangements and mutations have already been established in certain tumor types, we were more interested in looking at the more common FGFR alteration, that being amplifications. However, the efficacy in that was a little unknown, and so these two separate subprotocols were developed: K2, which was to look at FGFR mutations and fusions in tumor types, excluding urothelial carcinoma, to look if there was a signal of efficacy beyond currently FDA-approved indications, and amplification as a separate cohort.

Dr. Rafeh Naqash: That's a very good explanation of why you concentrated on the tumor types in these protocols.

Now, going back to subprotocol K1, could you tell us what were some of the tumor types that you did include, and what was the sample size, and what was the hypothesis for the sample size as a meaningful level of activity that you wanted to see and would have potentially led to a bigger, broader trial?

Dr. Jun Gong: So, subprotocol K1 was the arm investigating erdafitinib in those with FGFR amplifications, and these were predefined on the NCI-MATCH protocol, looking at FGFR 1, 2, 3, and 4 amplifications essentially. These were allowed to have local testing through a local CLIA-certified assay, but then they needed to be confirmed on a central assay, which is the NCI-MATCH Oncomine assay. These statistics are uniform for the NCI-MATCH trials, and the goal was at least 31 patients, with the hypothesis that if the response rate was 16% or more, this was considered a signal of activity. However, there was an additional protocol specific requirement in that if the sample size was fewer than 31 patients, then the primary efficacy population would be assessed against a null hypothesis overall response rate of 5%. Meaning that if there were less than 31 subjects, an overall response rate of greater than 5% would be defined as positive. Again, the NCI-MATCH was uniform. Secondary objectives included progression-free survival, overall survival, and safety and toxicity. With that being said, K1 originally began accrual. The NCI-MATCH actually launched in 2015, but in the subprotocol K1, 35 patients were initially enrolled in the study. If you go down the eligibility criteria, however, a lot of these patients dropped out due to a lack of central tumor confirmation and various reasons. Ultimately, 18 patients were included in the pre-specified primary efficacy cohort.

Dr. Rafeh Naqash: Thank you. I did see for subprotocol K1, you mostly had stable disease in a couple of patients, no responses, and I think one individual with breast cancer had a prolonged stable disease.

Now, from an FGFR amplification standpoint, did you or were you able to correlate - again, this is not objective responses, it's not a partial response or a complete response - was there any correlation from the level of amplification to the duration of stable disease?

Dr. Jun Gong: That's actually the core of our discussion about why K1, despite a variety basket of solid tumor types, somewhere, preclinical data had suggested FGFR amplifications could be targeted, that K1 was ultimately a negative trial with a 0% response rate. We dive in that although we included as an eligibility criteria a copy number variation of seven as the threshold for amplification, we realized that if you look at some of the literature out there, that even in the FGFR 1 and 2 amplification cohorts, where these are the more common cohorts of amplified tumor types that have been targeted, you really needed a high level of amplification, more than 99% of tumor cells being amplified in the previous studies, to actually generate a response.

The thought was that we assumed that FGFR amplification would lead to protein expression and dependence on FGFR signaling, providing sensitivity to FGFR inhibition. However, we realized that there is a certain degree where a high level of amplification needs to happen, and it may not be for all FGFR amplifications. We looked into the literature that FGFR 1 and 2 were the more commonly studied FGFR amplifications. FGFR 1, if you actually look at the amplicon structure, it tends to amplify a lot of other genes because it's such a huge amplicon structure. But FGFR 2 is shorter and centered on just FGFR 2 with a few other genes co-amplified. So, actually in the literature, they've already been seeing that maybe FGFR 2 amplification tumors are more readily targetable based on the robustness of evidence, rather than FGFR 1. But across all of these, the higher the level of amplification, seems the more targetable.

Dr. Rafeh Naqash: Those are interesting discussions around protein expression on the tumor that could imply therapeutic vulnerability. So I've always thought about it, whether trials like NCI-MATCH trials or ASCO TAPUR, for example, would be perhaps more informative if, on a secondary analysis standpoint, proteomics is something that could be done on the tumor tissue, because similar to NCI-MATCH, ASCO TAPUR has other sub protocols where some of these mutations or amplifications don't necessarily result in antitumor responses. But I think from a biology standpoint, as you mentioned, a certain amplification might correspond to RNA expression and that might correspond to protein expression, which is downstream. So looking at that would be something interesting. Have you planned for something like that on these tumor specimens? If you have biobanked any of those specimens.

Dr. Jun Gong: I think that's a great future direction. And I know you, Dr. Naqash, being involved in so many cooperative trials, I think it is possible, but it really depends on good trial planning from the onset. When designing such massive trials like this, I think the more important thing is if your trials are negative, but they are informative for the field to go back and have these postdoc available biobanks that you said. And I think having it integrated firstly, is way more efficient than to have kind of an amendment kind of going through halfway or when the trial is started. That could be a little bit more logistically difficult.

Dr. Rafeh Naqash: I completely agree. And you mentioned corporate groups, I think we've been discussing, and I'm pretty sure you have also, there's a lot to be learned from clinical trials that are negative. We often, in the academic or non-academic setting, end up not publishing some of those negative results, pharma or corporate group based studies. And I think the resources, the specimens, and the negative results could correlate to some other novel findings if some of those exploratory analyses are done in the appropriate manner.

Now, going to the drug itself or the erdafitinib here, it's a pan-FGFR inhibitor. Is that something that you think is a limitation in the drug development space? I do early phase trials, and I'm pretty sure you do a lot of these basket early phase trials. Is that something that you feel is a limitation when you have a drug that targets different mutations or different protein changes of the same gene or different amplifications? Could that be a reason why something like this doesn't necessarily work because it doesn't have as much specificity against the isoform as one might need to inhibit the downstream kinase activation?

Dr. Jun Gong: That is also a great point. The NCI-MATCH sub protocol K1 and K2 used erdafitinib, which was the first FDA-approved FGFR inhibitor. But as many of the listeners and yourself may know, there have been newer iterations in next-generation development of the FGFR inhibitors. And it's very fascinating, the tyrosine kinase inhibitors, with each iteration, you seem to have a little more potency and the ability to bypass some of the resistance mutations, almost paralleling the lung cancer space, where we kind of follow that, and they've been kind of the pioneers in that space. And to your point, yes, we consider– the NCI-MATCH was developed nearly a decade ago, and the available agents at that time, would it have changed the findings if we used a kind of a newer generation or more potent FGFR inhibitor? It's possible, I think, especially in the K1 cohort with the amplifications. We even suggested in the discussion of the paper future directions, is that one way to kind of bypass the amplification issue is to use more potent and specific FGFR inhibitors. And so I think it's very possible that you highlight this point.

Dr. Rafeh Naqash: And for the sake of our listeners, Jun, especially trainees, could you highlight what are currently some of the FDA-approved FGFR inhibitors, and what tumor types are they currently approved in?

Dr. Jun Gong: The first one, as we have hinted, was in treatment of refractory, essentially urothelial carcinoma with FGFR mutations and rearrangements, mainly 2 and 3. And this is where oral erdafitinib was approved. And it's interesting, I kind of teach my fellows and our health staff that erdafitinib is interesting in that its FDA label insert requires a starting dose of about 8 milligrams daily, and it's a 28-day cycle. But during the first 14 days, we're really looking at the serum phosphate levels. If they are within a certain level, if they are within 5.5 to 7, for example, you continue the current dose. But if they are less than 5.5, the FDA label actually mandates that you increase it to 9 milligrams oral daily, continuously. This is biologically logical to me. FGFR is located to the renal tubules, and so this is a major phosphate kind of metabolism pathway here. And so you're using that as a surrogate, essentially, if the right dosing is achieved. And so that's unique.

And then the subsequent kind of FGFR inhibitors that came about, you had a couple in cholangiocarcinoma, where, unlike urothelial carcinoma, where it's about 30% of the time, you'll find the FGFR alterations of target. It's about half of that 15% in cholangiocarcinoma, and it's mainly intrahepatic cholangiocarcinoma in that sense. And here you have pemigatinib, which is one of the FGFR inhibitors approved for cholangiocarcinoma. And then you also had infragatinib, which is approved. But however, infigratinib eventually had their FDA label culled. It was withdrawn by the company, I think it was in 2022. And then more recently, you had even a more potent FGFR inhibitor in cholangio approved and futibatinib. It's interesting that with these more later generations of FGFR inhibitors, they do show a correlation with phosphate levels, but they don't have that specific kind of dosing early on in the first cycle, like erdafitinib. And so it's interesting to see that with the later generations, you're seeing more potency as well.

Dr. Rafeh Naqash: Thank you for that overview, which I'm sure most of the trainees appreciate since this is an up and coming field in the space of precision medicine, especially FGFR. From a side-effect profile standpoint, you mentioned phosphate issues. Do you think that is a drug class effect here, or is that an FGFR receptor subtype effect, depending on which FGFR receptor, 1 or 2 or 3, that is being targeted?

Dr. Jun Gong: I do think this is a class effect that you'll see across a lot of the trials where phosphorus elevations or decreases are going to be probably your most common treatment-related adverse event. And I actually emphasize this is probably one of the most trickier side effects of this class, where we’re almost having to have to monitor the phosphorus levels pretty routinely, pretty closely. And you also have other class effects on the nails. There's some rare retinal ocular toxicities that's unique to the FGFR class as well. And so it's a very exciting class of compounds, but it does require some close monitoring of some unique class effects as you’ve hinted.

Dr. Rafeh Naqash: Based on the results from your K1 sub protocol, are FGFR inhibitors still the approach within, let's say, within cholangio or urothelial with FGFR amplifications? Is that still something that has been established and seen from a clinical response standpoint?

Dr. Jun Gong: The FDA approvals are really for mutations and fusions. So this K1 sub protocol, essentially, I think provides one answer that we've been all wondering about for the longest time, “Hey, could amplifications be targeted as well?” Unfortunately, we didn't include urothelial carcinomas in this study because of the FDA approval. But from a kind of a basket solid tumor perspective, I think this really dampens the enthusiasm. As of right now, it really is fusions and mutations that are targetable. Amplifications need further investigation before becoming established in solid tumors.

Dr. Rafeh Naqash: Going to the discussion with the second K2 protocol, which is mutations and fusions, can you highlight again which tumor types there where you saw some clinical outcomes that you saw and any unique insights on certain mutations or protein changes that were a little more relevant than some others?

Dr. Jun Gong: Sure. So this is the parallel study to K1, in that now we are looking at fusions and mutations of FGFR1, 2, 3, and 4. And essentially, we, again, excluded those with urothelial carcinoma, given the FDA approval for erdafitinib in this trial. The trial actually opened then the FDA approvals for the FGFR inhibitors for cholangiocarcinoma happened. So this trial didn’t really exclude those with FGFR mutated or rearranged cholangiocarcinoma as well. If you look at the breakdown of the cohort in K2, you saw a good mix of breast cancers or a couple of gynecologic malignancies. There were a couple of head and neck cancers. There were several brain tumors as well. There was one lung cancer. There were four noted intrahepatic cholangiocarcinomas. Again, we could not exclude those due to the fact that the trial had opened and was accruing when the FGFR inhibitors approved for cholangiocarcinoma happened. Similar design, with a phase II, single-arm, open-label of erdafitinib, and again, the same statistical design was implemented in that if it’s higher than 31 patients, 16% overall response rate was a primary endpoint goal. If it was less than that, it was against the 5% overall response rate.

And here in K2, 35 patients were enrolled and 25 patients were ultimately included in the primary efficacy analysis. So because it was fewer than 31 in the primary efficacy cohort, it followed the NCI-MATCH to be specified with a primary endpoint goal of 5% or higher. And here, in a heavily pre-treated cohort of more than 50% of subjects who have received prior than 3 or higher lines of therapy, overall response rate essentially confirmed was 16% with the p value of 0.034, which met the positivity cutoff of 5%. However, an additional seven patients experienced stable disease as best confirmed response. And it’s important to note that four of these were grade IV glioblastomas with prolonged progression-free survival. So ultimately, this trial was positive in reading the endpoint that outside of urothelial carcinoma, could FGFR inhibition be pursued in other tumor types that had FGFR rearrangements or fusions?

Dr. Rafeh Naqash: You mentioned glioblastoma, which is an area of huge unmet need. Do you think a trial like this as an upfront approach in glioblastoma, perhaps maybe after Temodar, could be a more meaningful way using the strongest, more precise therapy earlier on when there are certain mechanisms that inhibition of which would result in anti-tumor responses? Do you think doing this earlier on rather than second, third, fourth line would be more intriguing in some ways?

Dr. Jun Gong: I think you’ve hit upon several key points there. Firstly, just a high unmet need in glioblastomas, in general. And then to us, although it was a stable disease it was quite noticeable that four of these occurred in IDH1 and 2 wild-type brain tumors. We kind of discussed that in the discussion as well. And of these, we actually realized that in the pre-clinical and other published literatures space that for some reason, IDH1 and wild-type tended to have more FGFR alterations, while 0% were found in IDH1 and 2 mutant high grade gliomas. So I think there is something hypothesis generating coming out of this study as well even though there were stable disease. And that you may be selecting for– We may be able to have future studies to select for a specific niche of glioblastomas. And as to your point, Dr. Naqash, I think if we can have a design trial looking for these specific molecular subsets, I think it’s wide open for trials of this nature in the first line, second line, or refractory space. Even piggybacking into cholangiocarcinoma, you see, they’re now looking at these in the neoadjuvant and adjuvant space as well. So I think we can identify the subset - it’s wide open out there.

Dr. Rafeh Naqash: I completely agree. I remember my program director a few years back when immunotherapy was in the metastatic setting, it was very exciting. He gave a talk in which he said "Early, earlier, earliest," and the more early, the better it seems. So I'm guessing that it's probably something similar for precision medicine-based approaches like targeting FGFR perhaps earlier.

So what is next for some of these two studies, or these ideas that have come out of these two studies? Are you trying to develop something subsequently, or is NCI-MATCH looking at it from a certain perspective? Or what would you want to do as a next step, ideally if you had the funding and the pharma support?

Dr. Jun Gong: That’s the million dollar question. So just from the broad strokes, I think what these two back to back papers and studies comment is that amplifications may not be the more targetable of FGFR subset, but there is avenue for improvement there and further investigation. FGFR fusions and mutations however seem to go along with what we know in some of the FDA approved types now. Now the next step is in the area of precision oncology is could we expand the label indications now to other subtypes with FGFR fusions and mutations. And this is I think following precedent. You and the audience may know that there are a lot of different tumor agnostic approvals now for both immunotherapy and other targeted therapy types. So I think the goal of this study was to provide momentum for, perhaps, advancements into a tumor agnostic indication for FGFR inhibitors.

And we do cite in the K2 manuscript the results of a phase II study that was also published around the time we were writing the study up. It was the phase II RAGNAR study. And that enrolled patients, again, with FGFR fusions and mutations. And that trial was positive, too. That one was a larger study of 217 subjects. We highlight some differences in study populations as to why maybe the difference in responders were detected. Both were positive studies. It was reassuring that the overall survival impulse studies were about the same. And again, I think they don’t compete. I rather think they complement each other in providing this body of evidence that may meet- at one point, the FDA should be approached with this evidence for a tumor agnostic mutation so that more patients with this subset could be benefitting.

Dr. Rafeh Naqash: Excellent. Thank you so much, Jun.

Now, could you tell us briefly what your background is, where you’ve trained, and your interests, and how you balance clinical research with some of your personal interests?

Dr. Jun Gong: Sure. Thank you for that interest. I did my training in medical school in New York. I went to New York Medical College. And then I did my residency at Cedars-Sinai for medicine. And I went to City of Hope for fellowship where I was trained in GU by Dr. Monty Powell who maybe you folks are familiar with. And my GI training was with Dr. Fakih at City of Hope. And since then I returned back to Cedars-Sinai where I serve as a dual GI/GU focused medical oncologist. I do clinical trials in both and translational science, really focused on targeting tumor metabolism in both as well. My advice to the listeners and trainees and I tell my own fellows this, I think it’s very rare now unless you’re in phase I to do a dual focus. So I actually emphasized to my trainees that the more focused you can be, the better. Unless you are going into phase I, for example. With that, you can hone in, develop your craft. But then again, I have known several mentors who do multiple tumor types. But I think the more traditional mechanism is to focus as much as you can is my advice for the listeners.

Dr. Rafeh Naqash: Thank you again, Jun, for all those interesting scientific and personal insights. We appreciate you and working with JCO Precision Oncology for both of your manuscripts. This is the first time we have ever invited a lead author for two manuscripts at the same time. It's always good to be the first in something, and I learned a lot and hopefully, our audience would have learned a lot.

Dr. Jun Gong: Thank you, Dr. Naqash, for having me. It was a pleasure speaking with you and the crew.

Dr. Rafeh Naqash: Thank you.

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Phase II Study of Erdafitinib in Tumors with FGFR Amplifications and Mutations or Fusions

JCO Precision Oncology Conversations