Authors Drs. Jessica Ross and Alissa Cooper share insights into their JCO PO article, "Clinical and Pathologic Landscapes of Delta-Like Ligand 3 and Seizure-Related Homolog Protein 6 Expression in Neuroendocrine Carcinomas" Host Dr. Rafeh Naqash and Drs. Ross and Cooper discuss the landscape of Delta-like ligand 3 (DLL3) and seizure-related homolog protein 6 (SEZ6) across NECs from eight different primary sites.

TRANSCRIPT

Dr. Rafeh Naqash: Hello and welcome to JCO Precision Oncology Conversations, where we bring you engaging conversations with authors of clinically relevant and highly significant JCO PO articles. I'm your host, Dr. Rafeh Naqash, podcast editor for JCO PO and an Associate Professor at the OU Health Stephenson Cancer Center.

Today, I'm excited to be joined by Dr. Jessica Ross, third-year medical oncology fellow at the Memorial Sloan Kettering Cancer Center, as well as Dr. Alissa Cooper, thoracic medical oncologist at the Dana-Farber Cancer Institute and instructor in medicine at Harvard Medical School. Both are first and last authors of the JCO Precision Oncology article entitled "Clinical and Pathologic Landscapes of Delta-like Ligand 3 and Seizure-Related Homolog Protein 6 or SEZ6 Protein Expression in Neuroendocrine Carcinomas."

At the time of this recording, our guest disclosures will be linked in the transcript.

Jessica and Alissa, welcome to our podcast, and thank you for joining us today.

Dr. Jessica Ross: Thanks very much for having us.

Dr. Alissa Cooper: Thank you. Excited to be here.

Dr. Rafeh Naqash: It's interesting, a couple of days before I decided to choose this article, one of my GI oncology colleagues actually asked me two questions. He said, "Rafeh, do you know how you define DLL3 positivity? And what is the status of DLL3 positivity in GI cancers, GI neuroendocrine carcinomas?" The first thing I looked up was this JCO article from Martin Wermke. You might have seen it as well, on obrixtamig, a phase 1 study, a DLL3 bi-specific T-cell engager. And they had some definitions there, and then this article came along, and I was really excited that it kind of fell right in place of trying to understand the IHC landscape of two very interesting targets.

Since we have a very broad and diverse audience, especially community oncologists, trainees, and of course academic clinicians and some people who are very interested in genomics, we'll try to make things easy to understand. So my first question for you, Jessica, is: what is DLL3 and SEZ6 and why are they important in neuroendocrine carcinomas?

Dr. Jessica Ross: Yeah, good question. So, DLL3, or delta-like ligand 3, is a protein that is expressed preferentially on the tumor cell surface of neuroendocrine carcinomas as opposed to normal tissue. It is a downstream target of ASCL1, and it's involved in neuroendocrine differentiation, and it's an appealing drug target because it is preferentially expressed on tumor cell surfaces. And so, it's a protein, and there are several drugs in development targeting this protein, and then Tarlatamab is an approved bi-specific T-cell engager for the treatment of extensive-stage small cell lung cancer in the second line. SEZ6, or seizure-like homolog protein 6, is a protein also expressed on neuroendocrine carcinoma cell surface. Interestingly, so it's expressed on neuronal cells, but its exact role in neuroendocrine carcinomas and oncogenesis is actually pretty poorly understood, but it was identified as an appealing drug target because, similarly to DLL3, it's preferentially expressed on the tumor cell surface. And so this has also emerged as an appealing drug target, and there are drugs in development, including antibody-drug conjugates, targeting this protein for that reason.

Dr. Alissa Cooper: Over the last 10 to 15 years or so, there's been an increasing focus on precision oncology, finding specific targets that actually drive the cancer to grow, not just within lung cancer but in multiple other primary cancers. But specifically, at least speaking from a thoracic oncology perspective, the field of non-small cell lung cancer has completely exploded over the past 15 years with the discovery of driver oncogenes and then matched targeted therapies.

Within the field of neuroendocrine carcinomas, including small cell lung cancer but also other high-grade neuroendocrine carcinomas, there has not been the same sort of progress in terms of identifying targets with matched therapies. And up until recently, we've sort of been treating these neuroendocrine malignancies kind of as a monolithic disease process. And so recently, there's been sort of an explosion of research across the country and multiple laboratories, multiple people converging on the same open questions about why might patients with specific tumor biologies have different kind of responses to different therapies.

And so first this came from, you know, why some patients might have a good response to chemo and immunotherapy, which is the first-line approved therapy for small cell lung cancer, and we also sort of extrapolate that to other high-grade neuroendocrine carcinomas. What's the characteristic of that tumor biology? And at the same time, what are other targets that might be identifiable? Just as Jesse was saying, they're expressed on the cell surface, they're not necessarily expressed in normal tissue. Might this be a strategy to sort of move forward and create smarter therapies for our patients and therefore move really into a personalized era for treatment for each patient? And that's really driving, I think, a lot of the synthesis of this work of not only the development of multiple new therapies, but really understanding which tumor might be the best fit for which therapy.

Dr. Rafeh Naqash: Thank you for that explanation, Alissa. And as you mentioned, these are emerging targets, some more further along in the process with approved drugs, especially Tarlatamab. And obviously, DLL3 was something identified several years back, but drug development does take time, and readout for clinical trials takes time.

Could you, for the sake of our audience, try to talk briefly about the excitement around Tarlatamab in small cell lung cancer, especially data that has led to the FDA approval in the last year, year and a half?

Dr. Alissa Cooper: Sure. Yeah, it's really been an explosion of excitement over, as you're saying, the last couple of years, and work really led by our mentor, Charlie Rudin, had identified DLL3 as an exciting target for small cell lung cancer specifically but also potentially other high-grade neuroendocrine malignancies.

Tarlatamab is a DLL3-targeting bi-specific T-cell engager, which targets DLL3 on the small cell lung cancer cells as well as CD3 on T cells. And the idea is to sort of introduce the cancer to the immune system, circumventing the need for MHC class antigen presentation, which that machinery is typically not functional in small cell lung cancer, and so really allowing for an immunomodulatory response, which had not really been possible for most patients with small cell lung cancer prior to this.

Tarlatamab was tested in a phase 2 registrational trial of about 100 patients and demonstrated a response rate of 40%, which was very exciting, especially compared with other standard therapies which were available for small cell lung cancer, which are typically cytotoxic therapies. But most excitingly, more than even the response rate, I think, in our minds was the durability of response. So patients whose disease did have a response to Tarlatamab could potentially have a durable response lasting a number of months or even over a year, which had previously not ever been seen in this in the relapsed/refractory setting for these patients.

I think the challenge with small cell lung cancer and other high-grade neuroendocrine malignancies is that a response to therapy might be a bit easier to achieve, but it's that durability. The patient's tumors really come roaring back quite aggressively pretty quickly. And so this was sort of the most exciting prospect is that durability of response, that long potential overall survival tail of the curve really being lifted up.

And then most recently at ASCO this year, Dr. Rudin presented the phase 3 randomized controlled trial which compared Tarlatamab to physician's choice of chemotherapy in a global study. And the choice of chemotherapy did vary depending on the part of the world that the patients were enrolled in, but in general, it was a really markedly positive study for response rate, for progression-free survival, and for overall survival. Really exciting results which really cemented Tarlatamab's place as the standard second-line therapy for patients with small cell lung cancer whose disease has progressed on first-line chemo-immunotherapy. So that has been very exciting. This drug was FDA approved in May of 2024, and so has been used extensively since then. I think the adoption has been pretty widespread, at least in the US, but now in this global trial that was just presented, and there was a corresponding New England Journal paper, I think really confirms that this is something we really hopefully can offer to most of our patients.

And I think, as we all know, that this therapy or other therapies like it are also being tested potentially in the first-line setting. So there was data presented with Tarlatamab incorporated into the maintenance setting, which also showed exciting results, albeit in a phase 1 trial, but longer overall survival than we're used to seeing in this patient population. And we await results of the study that is incorporating Tarlatamab into the induction phase with chemotherapy as well. So all of this is extraordinarily exciting for our patients to sort of move the needle of how many patients we can keep alive, feeling functional, feeling well, for as long as possible.

Dr. Rafeh Naqash: Very exciting session at ASCO. I was luckily one of the co-chairs for the session that Dr. Rudin presented it, and I remember somebody mentioning there was more progress seen in that session for small cell lung cancer than the last 30, 35 years for small cell, very exciting space and time to be in as far as small cell lung cancer.

Now going to this project, Jessica, since you're the first author and Alissa's the last, I'm assuming there was a background conversation that you had with Alissa before you embarked on this project as an idea. So could you, again, for other trainees who are interested in doing research, and it's never easy to do research as a resident and a fellow when you have certain added responsibilities. Could you give us a little bit of a background on how this started and why you wanted to look at this question?

Dr. Jessica Ross: Yeah, sure. So, as with many exciting research concepts, I think a lot of them are derived from the clinic. And so I think Alissa and I both see a good number of patients with small cell, large cell lung cancer, and then high-grade neuroendocrine carcinomas. And so I think this was really born out of a basic conversation of we have these drugs in development targeting these two proteins, DLL3 and SEZ6, but really what is the landscape of cancers that express these proteins and who are the patients that really might benefit from these exciting new therapies. And of course, there was some data out there, but sort of less than one would imagine in terms of, you know, neuroendocrine carcinomas can really come from anywhere in the body. And so when you're seeing a patient with small cell of the cervix, for example, like what are the chances that their cancer expresses DLL3 or expresses SEZ6? So it was really derived from this pragmatic, clinically oriented question that we had both found ourselves thinking about, and we were lucky enough at MSK, we had started systematically staining patients' tumors for DLL3, tumors that are high-grade neuroendocrine carcinomas, and then we had also more recently started staining for SEZ6 as well. And so we had this nice prospectively collected dataset with which to answer this question.

Dr. Rafeh Naqash: Excellent. And Alissa, could you try to go into some of the details around which patients you chose, how many patients, what was the approach that you selected to collect the data for this project?

Dr. Alissa Cooper: This is perhaps a strength but also maybe a limitation of this dataset is, as Jesse alluded to, our pathology colleagues are really the stars of this paper here because we were lucky enough at MSK that they were really forethinking. They are absolute experts in the field and really forward-thinking people in terms of what information might be needed in the future to drive treatment decision-making.

And so, as Jesse had said, small cell lung cancer tumor samples reflexively are stained for DLL3 and SEZ6 at MSK if there's enough tumor tissue. The other high-grade neuroendocrine carcinomas, those stains are performed upon physician request. And so that is a bit of a mixed bag in terms of the tumor samples we were able to include in this dataset because, you know, upon physician request depends on a number of factors, but actually at MSK, a number of physicians were requesting these stains to be done on their patients with high-grade neuroendocrine cancers of of other histologies. So we looked at all tumor samples with a diagnosis of high-grade neuroendocrine carcinoma of any histology that were stained for these two stains of interest. You know, I can let Jesse talk a bit more about the methodology. She was really the driver of this project.

Dr. Jessica Ross: Yeah, sure. So we had 124 tumor samples total. All of those were stained for DLL3, and then a little less than half, 53, were stained for SEZ6. As Alissa said, they were from any primary site. So about half of them were of lung origin, that was the most common primary site, but we included GI tract, head and neck, GU, GYN, even a few tumors of unknown origin. And again, that's because I think a lot of these trials are basket trials that are including different high-grade neuroendocrine carcinomas no matter the primary site. And so we really felt like it was important to be more comprehensive and inclusive in this study.

And then, methodologically, we also defined positivity in terms of staining of these two proteins as anything greater than or equal to 1% staining. There's really not a defined consensus of positivity when it comes to these two novel targets and staining for these two proteins. But in the Tarlatamab trials, for some of the correlative work that's been done, they use that 1% cutoff, and we just felt like being consistent with that and also using a sort of more pragmatic yes/no cutoff would be more helpful for this analysis.

Dr. Alissa Cooper: And that was a point of discussion, actually. We had contemplated multiple different schemas, actually, for how to define thresholds of positivity. And I know you brought up that question before, what does it mean to be DLL3 positive or DLL3 high? I think you were alluding to prior that there was a presentation of obrixtamig looking at extra-pulmonary neuroendocrine carcinomas, and they actually divvied up the results between DLL3 50% or greater versus DLL3 low under 50%. And they actually did demonstrate differential efficacy certainly, but also some differential safety as well, which is very provocative and that kind of analysis has not been presented for other novel therapies as far as I'm aware. I could be wrong, but as far as I'm aware, that was sort of the first time that we saw a systematic presentation of considering patients to be, quote unquote, "high" or "low" in these sort of novel targets.

I think it is important because the label for Tarlatamab does not require any DLL3 expression at all, actually. So it's not hinging upon DLL3 expression. They depend on the fact that the vast majority of small cell lung cancer tumors do express DLL3, 85% to 90% is what's been demonstrated in a few studies. And so, there's not prerequisite testing needed in that regard, but maybe for these extra-pulmonary, other histology neuroendocrine carcinomas, maybe it does matter to some degree.

Dr. Rafeh Naqash: Definitely agree that this evolving landscape of trying to understand whether an expression for something actually really does correlate with, whether it's an immune cell engager or an antibody-drug conjugate is a very evolving and dynamically moving space. And one of the questions that I was discussing with one of my friends was whether IHC positivity and the level of IHC positivity, as you've shown in one of those plots where you have double positive here on the right upper corner, you have the double negative towards the left lower, whether that somehow determines mRNA expression for DLL3. Obviously, that was not the question here that you were looking at, but it does kind of bring into question certain other aspects of correlations, expression versus IHC. Now going to the figures in this manuscript, very nicely done figures, very easy to understand because I've done the podcast for quite a bit now, and usually what I try to do first is go through the figures before I read the text, and and a lot of times it's hard to understand the figures without reading the text, but in your case, specifically the figures were very, very well done. Could you give us an overview, a quick overview of some of the important results, Jessica, as far as what you've highlighted in the manuscript?

Dr. Jessica Ross: Sure. So I think the key takeaway is that, of the tumors in our cohort, the majority were positive for DLL3 and positive for SEZ6. So about 80% of them were positive for DLL3 and 80% were positive for SEZ6. About half of the tumors were stained for both proteins, and about 65% of those were positive as well. So I think if there's sort of one major takeaway, it's that when you're seeing a patient with a high-grade neuroendocrine carcinoma, the odds are that their tumor will express both of these proteins. And so that can sort of get your head thinking about what therapies they might be eligible for.

And then we also did an analysis of some populations of interest. So for example, we know that non-neuroendocrine pathologies can transform into neuroendocrine tumors. And so we specifically looked at that subset of patients with transformed tumors, and those were also- the majority of them were positive, about three-quarters of them were positive for both of these two proteins. We looked at patients with brain met samples, again, about 70% were positive.

And then I'd say the last sort of population of interest was we had a subset of 10 patients who had serial biopsies stained for either DLL3 or SEZ6 or both. In between the two samples, these patients were treated with chemotherapy. They were not treated with targeted therapy, but interestingly, in the majority of cases, the testing results were concordant, meaning if it was DLL3 positive to begin with, it tended to remain DLL3 positive after treatment. And so I think that's important as well as we think about, you know, a patient who maybe had DLL3 testing done before they received their induction chemo-IO, we can somewhat confidently say that they're probably still DLL3 positive after that treatment.

And then finally, we did do a survival analysis among specifically the patients with lung neuroendocrine carcinomas. We looked at whether DLL3 expression affected progression-free survival on first-line platinum-etoposide, and then we looked at did it affect overall survival. And we found that it did not have an impact or the median progression-free survival was similar whether you were DLL3 positive or negative. But interestingly, with overall survival, we found that DLL3 positivity actually correlated with slightly improved overall survival. These were small numbers, and so, you know, I think we have to interpret this with caution, for sure, but it is interesting. I think there may be something to the fact that five of the patients who were DLL3 positive were treated with DLL3-targeting treatments. And so this made me think of, like in the breast cancer world, for example, if you have a patient with HER2-positive disease, it initially portended worse prognosis, more aggressive disease biology, but on the other hand, it opens the door for targeted treatments that actually now, at least with HER2-positive breast cancer, are associated with improved outcomes. And so I think that's one finding of interest as well.

Dr. Rafeh Naqash: Definitely proof-of-concept findings here that you guys have in the manuscript.

Alissa, if I may ask you, what is the next important step for a project like this in your mind?

Dr. Alissa Cooper: Jesse has highlighted a couple of key findings that we hope to move forward with future investigative studies, not necessarily in a real-world setting, but maybe even in clinical trial settings or in collaboration with sponsors. Are these biomarkers predictive? Are they prognostic? You know, those are still- we have some nascent data, data has been brewing, but I think that we we still don't have the answers to those open questions, which I think are critically important for determining not only clinical treatment decision-making, but also our ability to understand sequencing of therapies, prioritization of therapies.

I think a prospective, forward-looking project, piggybacking on that paired biopsy, you know, we had a very small subset of patients with paired biopsies, but a larger subset or cohort looking at paired biopsies where we can see is there evolution of these IHC expression, even mRNA expression, as you're saying, is there differential there? Are there selection pressures to targeted therapies? Is there upregulation or downregulation of targets in response not just to chemotherapy, but for example, for other sort of ADCs or bi-specific T-cell engagers? I think those are going to be critically important future studies which are going to be a bit challenging to do, but really important to figure out this key clinical question of sequencing, which we're all contemplating in our clinics day in and day out. If you have a patient, and these patients often can be sick quite quickly, they might have one shot of what's the next treatment that you're going to pick. We can't guarantee that every patient is going to get to see every therapy. How can you help to sort of answer the question of like what should you offer? So I think that's the key question sort of underlying any future work is how predictive or prognostic are these biomarkers? What translational or correlative studies can we do on the tissue to understand clinical treatment decision-making? I think those are the key things that will unfold in the next couple of years.

Dr. Rafeh Naqash: The last question for you, Alissa, that I have is, you are fairly early in your career, and you've accomplished quite a lot. One of the most important things that comes out from this manuscript is your mentorship for somebody who is a fellow and who led this project. For other junior investigators, early-career investigators, how did you do this? How did you manage to do this, and how did you mentor Jessica on this project with some of the lessons that you learned along the way, the good and other things that would perhaps help other listeners as they try to mentor residents, trainees, which is one of the important things of what we do in our daily routine?

Dr. Alissa Cooper: I appreciate you calling me accomplished. Um, I'm not sure how true that is, but I appreciate that. I didn't have to do a whole lot with this project because Jesse is an extraordinarily smart, driven, talented fellow who came up with a lot of the clinical questions and a lot of the research questions as well. And so this project was definitely a collaborative project on both of our ends.

But I think what was helpful from both of our perspectives is from my perspective, I could kind of see that this was a gap in the literature that really, I think, from my work leading clinical trials and from treating patients with these kinds of cancers that I really hoped to answer. And so when I came to Jessica with this idea as sort of a project to complete, she was very eager to take it and run with it and also make it her own.

You know, in terms of early mentorship, I have to admit this was the first project that I mentored, so it was a great learning experience for me as well because as an early-career clinician and researcher, you're used to having someone else looking over your shoulder to tell you, "Yes, this is a good journal target, here's what we can anticipate reviewers are going to say, here are other key collaborators we should include." Those kind of things about a project that don't always occur to you as you're sort of first starting out. And so all of that experience for me to be identifying those more upper-level management sort of questions was a really good learning experience for me. And of course, I was fantastically lucky to have a partner in Jesse, who is just a rising star.

Dr. Jessica Ross: Thank you.

Dr. Rafeh Naqash: Well, excellent. It sounds like the first of many other mentorship opportunities to come for you, Alissa. And Jessica, congratulations on your next step of joining and being faculty, hopefully, where you're training.

Thank you again, both of you. This was very insightful. I definitely learned a lot after I reviewed the manuscript and read the manuscript. Hopefully, our listeners will feel the same. Perhaps we'll have more of your work being published in JCO PO subsequently.

Dr. Alissa Cooper: Hope so. Thank you very much for the opportunity to chat today.

Dr. Jessica Ross: Yes, thank you. This was great.

Dr. Rafeh Naqash: Thank you for listening to JCO Precision Oncology Conversations. Don't forget to give us a rating or review and be sure to subscribe so as you never miss an episode. You can find all ASCO shows at asco.org/podcasts.

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.

Disclosures:

Dr. Alissa Jamie Cooper

Honoraria
Company: MJH Life Scienes, Ideology Health, Intellisphere LLC, MedStar Health, Physician's Education Resource, LLC, Gilead Sciences, Regeneron, Daiichi Sankyo/Astra Zeneca, Novartis,

Research Funding: Merck, Roche, Monte Rosa Therapeutics, Abbvie, Amgen, Daiichi Sankyo/Astra Zeneca

Travel, Accommodations, Expenses: Gilead Sciences

DLL3 and SEZ6 Expression in Neuroendocrine Carcinomas

JCO Precision Oncology Conversations