Botensilimab Plus Balstilimab in Advanced Sarcomas
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Dr. Shannon Westin and her guest, Dr. Breelyn Wilky, discuss the JCO article, "“Botensilimab (Fc-enhanced anti-cytotoxic lymphocyte-association protein-4 antibody) Plus Balstilimab (anti-PD-1 antibody) in Patients With Relapsed/Refractory Metastatic Sarcomas."

TRANSCRIPT 

Shannon Westin: Hello, everyone, and welcome to another episode of JCO After Hours, the podcast where we get in depth on research that has been published in the Journal of Clinical Oncology. I am your host, Gynecologic Oncologist and Social Media Consultant Editor of the JCO, Shannon Westin. I serve here from the University of Texas MD Anderson Cancer Center. And I am so excited to welcome Dr. Breelyn Wilky. She's an Associate Professor and the Director of Sarcoma Medical Oncology in the Department of Medicine Division of Medical Oncology, and the Cheryl Bennett & McNeilly family endowed chair in Sarcoma Research, the Deputy Associate Director of Clinical research at the University of Colorado Cancer Center.

Welcome.

Dr. Breelyn Wilky: Thank you so much. I'm delighted to be here.

Shannon Westin: And with all those titles, I'm super impressed that she was able to complete the manuscript that we're going to discuss today, which is “Botensilimab (Fc-enhanced anti-cytotoxic lymphocyte-association protein-4 antibody) Plus Balstilimab (anti-PD-1 antibody) in Patients With Relapsed/Refractory Metastatic Sarcomas.” And this was published in the JCO on January 27, 2025.

And please note, our participants do not have any conflicts of interest.

So this is exciting. Let's first level set. Can you review with us just the current state of sarcoma incidents, survival outcomes, that kind of thing so we all know where we're starting?

Dr. Breelyn Wilky: Yes. So, you know, sarcomas are really, I like to call them the black box cancer type. And the big thing is that there's really more than a hundred different kinds of sarcomas, which collectively altogether make up only 1% of adult cancers. And so we talk about these as being bone and soft tissue tumors, but really, the heterogeneity is just incredible. You're talking maybe 10,000 to 12,000 new cases of soft tissue sarcoma per year, which is pretty rare in the grand scheme of things. And the trouble with these is that while you can cure sarcomas if you find them early and they're localized, when they metastasize and spread and are not resectable, we're looking at median overall survivals of really only 12 to 18 months, even, you know, with our best therapies that we have. So, really there's just a dire need for new treatments for this really tough group of diseases.

Shannon Westin: Yeah, I agree. I'm a gynecologic oncologist, and we have our little subset of sarcomas that I know there's a little bit out of every one. So I'm really excited to pull this manuscript as one of our podcasts offerings because I think we're all seeing these patients in the clinic and certainly our listeners that have sarcoma or have family members with sarcoma, this is so good to have a real focus on a rare group of tumors that have been a little bit lumped together.

Now, with that being said, I know this is such a heterogeneous population, but can you briefly overview a little bit around the standard of care for treatment of recurrent sarcomas?

Dr. Breelyn Wilky: We have actually been using the same drugs really since about the 1970s, and up until very recently, nothing had really challenged doxorubicin, the old ‘red devil’, like we used to call it. And this has been the mainstay of treatment for metastatic sarcomas and really used across the board. In the GYN literature, for uterine leiomyosarcoma, we did see some promising activity with the combination of doxorubicin and trabectedin coming out of the French group. But, except for that study, no combination therapy or new drug has been proven better in terms of overall survival compared to doxorubicin monotherapy, really over 40, 50 years. So it's definitely a tough situation.

Now, we do have other drugs that we use, so most patients will wind up getting doxorubicin-based therapy. There's a couple of other regimens that we'll reach to, like gemcitabine docetaxel. And once you get into the specific subtypes, we have some approvals in liposarcomas and leiomyosarcomas for some other drugs. But really the median progression for survival for most of these regimens is somewhere four to six months. And response rates typically are somewhere like 10%, 15% for most of these. So it's really just a very tough field and a tough group of patients to try to make an impact for.

Shannon Westin: So let's talk a little bit more kind of getting focused on what you've studied here. What's been the role of immunotherapy thus far in the treatment of sarcomas maybe prior to this particular study?

Dr. Breelyn Wilky: Clearly, we all know that immune therapy has just changed cancer care forever over the last few years for so many different types of cancers and diseases like melanoma and renal cell and lung cancer have just been transformed by checkpoint inhibitors specifically directed against PD-1 or CTLA-4 or both. And so, of course, you know, sarcoma docs we're super excited to try to see if these might potentially have activity in our tumors as well. I never had seen myself in my career getting into immunotherapy until I was able to run an investigator-initiated study during my role in Miami, where we combined pembrolizumab, so PD-1 inhibitor, with axitinib which was a pan-VEGF inhibitor. And lo and behold, like I had patients that I was seeing responses when other treatments, all those chemotherapies I was just talking about had failed. And one of my first patients I treated was about a 60-year-old lady with something called cutaneous angiosarcoma. So this is a blood vessel sarcoma all over her face. And we had treated her with 10 different therapies, all the chemotherapy regimens, targeted therapies, clinical trials, and nothing was working. But I put her on a phase 1 trial with a baby dose of CTLA-4 and this woman had a complete response. And so for me, once I saw it work in even just those couple of patients, like that was nothing that we'd ever seen with our chemotherapy regimens. And so that sort of shifted my career towards really focusing on this, and this is about the time where some of the studies started to come out for sarcomas.

And the take home with sarcoma is about 20% of sarcomas have this sort of immune hot physiology. So what that basically means is if you look at gene expression of immune related gene signatures, or you look for infiltrating T-cells, sort of the SWAT team of our immune system, like you can find those in the tumors. And it's sort of evidence that the immune system had some clue for that 20% of patients that this was a foreign tumor and that it should be attacking it and maybe just needed a little help.

But globally, about 80% of sarcomas are these immune cold tumors, which means the immune system has no clue that these things are even a threat. And there's almost no immune activation, very, very few antigens. In other cancer types, high neoantigens or tumor antigens help the immune system work better. And so that basically goes with what we've seen with trials of PD-1 or CTLA-4 blockade. About 20% of sarcomas, with some exceptions, can respond. But really 80% across the board, you're stuck, you just can't get them to be recognized. And so that's where I think this data is so interesting is there's some signals of activity in these immune cold tumors which, at least historically with the trials we've done so far, we really haven't seen that with sort of the traditional checkpoints.

Shannon Westin: So I think now this is a great time to maybe talk about the study design in general, the eligibility and just give us kind of a run through of that.

Dr. Breelyn Wilky: So this trial was a phase 1 trial of a drug called botensilimab, which is a next generation CTLA-4 directed immune modulator. So what makes botensilimab different is that the CTLA-4 end is very similar to other CTLA-4 inhibitors that are out there, but it's been engineered on the back end of the molecule that binds to Fc gamma receptors to basically bind tighter with higher affinity. And what this translates to in laboratory models and increasingly now in patients is it does a better job of priming, of educating our T cells, our, again, these highly intelligent antigen specific cells, but also natural killer cells. It does a better job of sort of educating those. It helps to activate macrophages and other supporting actors in the immune response. And so the idea here is that there's evidence that botensilimab may do a better job at creating new responses in immune cold tumors.

The study combined either botensilimab as monotherapy or in combination with a PD-1 inhibitor called balstilimab. And this was all comers, really a variety of tumor types. And to date I think we're close to about 500 patients with a variety of solid tumors that have been accrued to this study, this C-800-01 phase 1 trial. This paper reports on the sarcoma patients that were enrolled as part of this study. And so, again, given what I've told you about sarcomas being really immune cold, we were just so excited to have the opportunity to enroll on a next generation immune therapy for these tumors that really we were running into roadblocks trying to use immunotherapy previously.

Shannon Westin: It's a very compelling idea and I'm so excited for you to tell people what you found. I think first things first, it was an early phase trial. So why don't we talk a little bit about the safety of the regimen. Was there anything that you didn't expect?

Dr. Breelyn Wilky: Right. So similar to other checkpoint inhibitors, you know, the idea is that these drugs can cause immune mediated toxicities, right? So essentially you're revving up the immune system and it can sometimes get a bit confused and start attacking our normal cells, our normal organs, leading to essentially any number of toxicities of basically head to toe, something can get inflamed and you can develop a toxicity from that. So the key take homes with this particular drug with, botensilimab with balstilimab, we saw colitis was sort of the primary immune mediated toxicity and it was about a third of patients, give or take. It happens and it can be aggressive and needs to be managed aggressively. And you know, one of the things that we learned very quickly taking part in this study is how important it is that as soon as patients start to get diarrhea, immunosuppression gets on board. So steroids, early use of TNF alpha blockade, so infliximab for example, if we jumped on it quickly and we recognized it and we got the patients treated, it would resolve fairly quickly and even some patients could remain on treatment. So I think that was sort of the first take home is “Okay if you get colitis, you treat it fast, you treat it early and you can still have patients not only recover, which essentially everybody recovered from this colitis and then being able to continue on treatment and still have their anti-tumor responses.” So that's the first point.

The second thing that was really interesting is part of the engineering of botensilimab on the back end of the molecule, it's been designed to decrease complement binding and it's thought that that triggers some of these other toxicities that we've seen with prior CTLA-4 inhibitors like pneumonitis or hypophysitis. We actually don't see that with botensilimab. So there's sort of this selective toxicity that may reflect the design of the molecule. But overall the treatment was, we didn't see any new safety signals that were outside of what we would expect in class. And colitis was sort of the dominant thing that we had to be ready for and ready to manage.

Shannon Westin: We've been doing it for a while now, so we kind of know what to do and we can act quickly and really try to mitigate and avoid some of the major toxicities. So that's great that that was what was reflected in what you found. And then of course I think: What about the efficacy?” Right. This is what we care about as practitioners, as patients. Does it work and are there any subtypes that seem to benefit the most from this combination?

Dr. Breelyn Wilky: Right. So for the sarcoma patients, we treated 64 patients and 52 of those patients were evaluable for efficacy. So a decent size group of patients in sarcomas, where, you know, typically our trials are pretty small, they're very rare, but we had 52 evaluable with at least one post baseline scan. So that was our criteria. And basically we saw across all of the patients, and keep in mind, these are heavily pre-treated patients, as you mentioned, so a median of 3 prior lines of therapy, so most of these patients had had chemotherapies and then about 20% had also had prior immunotherapy as well. So PD-1 treatments or so on. The overall response rate by RECIST was 19.2% for all of the evaluable patients. And then with iRECIST, which is sort of that immune adapted response criteria that allows for early pseudo progression, we actually had another patient who did have that. And so that response rate was 21.2%. Overall, we were really excited to see this in a heavily pre-treated group of patients.

But what was really exciting to me was when we looked at the subset of patients that had angiosarcoma, that blood vessel tumor I was talking about earlier with my other patient. So angios come in two flavors. One is this sort of cutaneous type, or meaning involving the skin that has a UV signature, a UV damage signature, very similar to melanoma. So these tumors tend to have a high mutation burden. And oftentimes there is a track record that we've seen responses with immunotherapy in cutaneous angiosarcomas. But the other group that we deal with is called visceral angiosarcomas. And so these are totally different biologically. These are often driven by mutations in MYC or KDR amplification, and they arise in organs, so primary breast angiosarcoma, not associated with radiation, or they can arise in the liver or the spleen or an extremity. So these are very, very different tumors, and the visceral ones almost never historically have responded to checkpoint inhibitors. So we had 18 patients with angio split - 9 with cutaneous, 9 with visceral. And we were just blown away because the response rate for that group was 27.8%. And if you looked at the responses between the hot ones and the cold ones, it was almost equal and a little bit better in the visceral. So we had a 33% response rate in visceral angiosarcoma, which is crazy, historically speaking, and about 20% again in the cutaneous angios. So for a disease where visceral angio gets treated with chemotherapy, might respond initially, but then rapidly progresses - like these people go through multiple lines of therapy - to have a third of patients responding, and then some of those responses were durable. Our median duration of response for the study was 21.7 months, which is just nuts for sarcomas where we just don't see those sorts of long term benefits with the drugs that we have. So I think those are kind of the two main things.

There were other subtypes that had clinical benefit and responses as well in d-diff liposarcoma, soft tissue leiomyosarcoma, which are again thought to be fairly cold immune subtypes. So just really exciting to kind of see responses we hadn't expected in a very challenging group of tumors.

Shannon Westin: We see all these patients and we have patients that respond so well to immunotherapy with other histotypes. And so it's so exciting to see an option for these really hard to treat tumors that our patients struggle with. So this is so, so very exciting.

I wanted to make mention, you know, I was really impressed with the amount of translational work you were able to do in this early phase study. So do you want to review just maybe a few of the key findings that you guys discovered?

Dr. Breelyn Wilky: It's always great. I'm a translational researcher at heart and we do a lot of immune correlative work. And I think the reason I got so excited about this field to begin with was trying to learn why it works for some patients and why it doesn't work for other patients. So I'm a huge believer in learning from every patient that we can. So it's such a testament to the company, Agenus, who sponsored this trial to invest their time and resources into correlative studies at this phase. It's huge.

So we learned a couple of things. IL-6 or interleukin 6 is a cytokine that basically has, in other tumor types, been associated with worse outcomes. And what we were interested in this group is we saw the same thing. And again, sarcomas have very, very little correlative biology that's done. We're really in infancy and understanding the microenvironment and how that milieu balances out in our tumors. So we were really excited to see again that lower peripheral interleukin 6 associated with improved overall survival. So again, kind of sorting out a group of patients that might be immunologically favorable when it comes to this type of therapy.

The other thing that's important to know about sarcoma is so the other tumor types are lucky and have PD-L1 expression and the tumor is a biomarker, but we never have PD-L1 expression. We can find it in sarcomas and it can be loosely correlated with a chance of benefit with immunotherapy. But I've had patients respond that were PD-L1 negative, and I've had patients that were loaded with PD-L1 that didn't seem to make a difference. And that's not just in this study.

So we saw in this trial a trend towards improved overall survival with PD-L1 expression that wasn't significant, but there was like this trend. And it's really interesting because, again, this is largely a CTLA-4 directed therapy. And so what we wondered is if PD-L1 expression is an index of sort of this underlying potential immunogenicity. And actually PD-1 works very late in the whole immune process. That's really at the very end where you've got the T cell that's facing the tumor cell and it's just activating that T cell that's already grown up and already educated and ready to go. Whereas CTLA-4 is really educating in early immune responses and expanding the T cells that have potential to kill. So I'm interested to look into this in more depth in the future to see if this is actually the biomarker for CTLA-4 directed therapy that we've been looking for, because we really don't have a great sense about that.

And then the last piece just to note is that in this trial, like most others, very, very few sarcomas had high mutational burden. Everybody was very low, which reflects the population. And it's just really more encouragement than an immune cold tumor with very crappy neoantigens can still respond to immunotherapy if we get them the right agents.

Shannon Westin: Yeah, I mean, I'm taking notes because we have such a struggle with this across the gynecologic tumors. I'm like, “Okay, maybe this is finally it.” So hopefully your work will go on to really inspire us across a number of solid tumors that have been traditionally cold. So, so very exciting.

And I would just say for my last question, obviously, congratulations on this successful study. What do you think are the next steps for this combination in sarcomas?

Dr. Breelyn Wilky: So, again, just to your point, this trial enrolled a bunch of different subtypes, and sarcomas are not the only immune cold tumor that this combo has looked really promising for, microsatellite stable colorectal cancer, ovarian cancer that was platinum refractory, non-small cell lungs. So I think the future is really bright for immune cold tumors kind of across the board. So, yes, lots of hope for not just sarcomas but in terms of our patients, I just have to be so grateful to Agenus for their interest in a rare disease. Sometimes it's hard to get that interest for a very challenging group of patients that are all heterogeneous, they are not all the same and our big clinical trials are a few hundred patients. It's just a very different environment. But they have been so supportive and involved in making sure that sarcomas are represented in their priorities. So there are ongoing discussions about what the optimal way to explore this further in sarcomas is going to be and I cannot wait to have the official plans in place. But my hope is this will not be the last that we see of these drugs for our patients.

Shannon Westin: Well, I support that and my vote is on your side.

So, thank you so much again, Dr. Wilky. This time just flew by. This was such a great discussion and I mean, I think it's, again, a testament to your exciting data.

And thank you to all of our listeners. This has been JCO After Hours’ discussion of “Botensilimab (Fc-enhanced anti-cytotoxic lymphocyte-association protein-4 antibody) Plus Balstilimab (anti-PD-1 antibody) in Patients With Relapsed/Refractory Metastatic Sarcomas,” published in the JCO on January 27, 2025. So be sure to check out the full manuscript.

And we hope that you enjoyed this podcast. And if you want to hear more about research published in the JCO, check this out on our ASCO JCO website or 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.

Dr. Wilky Disclosures 

Consulting or Advisory Role: SpringWorks Therapeutics, Deciphera, Epizyme, Adcendo, Polaris, Boehringer Ingelheim, AADi, InhibRx Research Funding: Exelixis Travel, Accommodations, Expenses: Agenus