BRCA-Altered Uterine Sarcoma Treated with PARP Inhibitors
JCO PO author Dr. Alison M. Schram at Memorial Sloan Kettering Cancer Center shares insights into her JCO PO article, “Retrospective Analysis of BRCA-Altered Uterine Sarcoma Treated With Poly(ADP-ribose) Polymerase Inhibitors.” Host Dr. Rafeh Naqash and Dr. Schram discuss relevant genomic and clinical features of patients with BRCA-altered uterine sarcoma and the efficacy of PARPis in this population.
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 Precision Oncology and associate professor at the OU Health Stephenson Cancer Center.
Today, we are excited to be joined by Dr. Alison Schram, Associate Attending Physician and Section Head of Oral Therapeutics with Early Drug Development and Gynecologic Medical Oncology Services at the Memorial Sloan Kettering Cancer Center, and the senior author of the JCO Precision Oncology article titled, "Retrospective Analysis of BRCA-Altered Uterine Sarcoma Treated With Poly(ADP-ribose) Polymerase Inhibitors."
At the time of this recording, our guest's disclosures will be linked in the transcript.
Dr. Schram, thank you for joining us today. I am excited to be discussing this very interesting, unique topic based on what you published in JCO PO.
Dr. Alison Schram: Thank you for having me.
Dr. Rafeh Naqash: What we like to do for these podcasts is try to make them scientifically interesting but at the same time, keep them at a level where our trainees and other community oncology professionals understand the implications of what you've published. So I'd like to start by asking you, what is leiomyosarcoma for those of us who don't necessarily know a lot about leiomyosarcoma, and what are some of the treatment options for these uterine sarcomas?
Dr. Alison Schram: Uterine leiomyosarcoma is a rare subtype of uterine cancer, and it represents about 1% of all female cancers in the reproductive tract. This is a rare malignancy that arises from the myometrial lining of the uterus, and it is generally pretty aggressive. In terms of the standard therapy, the standard therapy for uterine leiomyosarcoma includes chemotherapy, generally combination chemotherapy, but despite a few regimens that tend to be effective, the duration of effectiveness is relatively short-lived, and patients with advanced uterine leiomyosarcoma eventually progress and require additional therapy. I will say that localized uterine leiomyosarcoma can be treated with surgery as well.
Dr. Rafeh Naqash: Thank you for that description. Now, there are two aspects to what you published. One is the sarcoma aspect, the leiomyosarcoma, and the second is the BRCA mutation. Since we are a precision medicine journal, although we've discussed BRCA a couple of times before, but again, for the sake of our listeners, could you highlight some of the aspects of BRCA and PARP sensitivity for us?
Dr. Alison Schram: Yes. So BRCA is a gene that's important for DNA repair, and BRCA mutations can be either inherited as a germline mutation, so one of your parents likely had a BRCA mutation and you inherited one copy. In patients who have an inherited BRCA mutation, the normal cells tend to have one abnormal copy of BRCA, but if a second copy in the cell becomes altered, then that develops into cancer. And so these patients are at increased risk of developing cancers. Specifically, they are at an increased risk of developing ovarian cancer, breast cancer, prostate cancer, pancreatic cancer, and a few others. These cancers are considered BRCA-associated tumors.
Alternatively, some patients, more rarely, can develop BRCA-altered cancers completely sporadically. So it's a mutation that happens in the tumor itself, and that can lead to impaired DNA repair and promote cancer progression. And those patients are not, they don't have any inherited risk, but just a random event caused a BRCA mutation in the tumor. The reason this is important is because, in addition to it being potentially important for family members, there are certain treatments that are more effective in BRCA-altered cancers. And the main example is PARP inhibitors, which are small molecule inhibitors that inhibit the PARP enzyme, and there is what we call synthetic lethality. So PARP is important for DNA repair, for single-stranded DNA repair, BRCA is important for double-stranded DNA repair, and in a patient that has a cancer that has a BRCA mutation, that cancer becomes more reliant on single-stranded DNA repair. And if you inhibit it with a PARP inhibitor, the cancer cells are unable to repair DNA, and the cells die. So we call that synthetic lethality. PARP inhibitors are FDA approved in several diseases, predominantly the BRCA-associated diseases I mentioned: breast cancer, ovarian cancer, pancreatic cancer, and prostate cancer.
Dr. Rafeh Naqash: That was very beautifully explained. Honestly, I've heard many people explain BRCA before, but you kind of put it in a very simple, easy to understand format.
You mentioned this earlier describing germline or hereditary BRCA and somatic BRCA. And from what I gather, you had a predominant population of somatic BRCA, but a couple of germline BRCA as well in your patient population, which we'll go into details as we understand the study. You mentioned the second hit on the germline BRCA that is required for the other copy of the gene to be altered. In your clinical experience, have you seen outside of the study that you published, a difference in the sensitivity of PARP for germline BRCA versus a somatic BRCA that has loss of both alleles?
Dr. Alison Schram: So we will get into what's unique about uterine sarcomas in just a minute. In uterine sarcomas, what we have found is that the BRCA mutations tend to be somatic and not germline, as you mentioned. That is in contrast to the other diseases we mentioned, where the vast majority of these tumors are in patients that have germline BRCA alterations. So one thing that's really unique about the uterine sarcoma population and our paper, I believe, is that it is demonstrating an indication for PARP inhibitors in a population that is not characterized by germline BRCA alterations, but truly these by somatic BRCA alterations.
If you look at the diseases that PARP inhibitors are validated to be effective in, including the, you know, the ones I mentioned, the BRCA-associated tumors, there's some data in specific context that suggests that perhaps germline alterations are more sensitive to PARP inhibitors, but that's not universal, and it's really tricky to do because the genetic testing that we have doesn't always tell you if you have two hits or just one hit. So you need more complex genetic analysis to truly understand if there is what we call a biallelic loss. And sometimes it's not a second mutation in BRCA. Sometimes it's silencing of the gene by hypermethylation or epigenetics. Some of our clinical trials are now incorporating this data collection to really understand if biallelic loss that we can identify on more complex genetic testing predicts for better outcomes. And we think it's probably true that the patients that have biallelic loss, whether it be germline or somatic biallelic loss, are more likely to benefit from these treatments. That still needs to be tested in a larger cohort of patients prospectively.
Dr. Rafeh Naqash: In your clinical experience, I know you predominantly use MSK-IMPACT, but maybe you've perhaps used some other NGS platforms, next-generation sequencing platforms. Have you noticed that these reports for BRCA alterations the report mentioning biallelic loss in certain cases? I personally don't- I do lung cancer, I do early-phase lung cancer as well, but I personally don't actually remember if I've seen a report that actually says biallelic loss. So after this podcast, I'm going to check some of those NGS reports and make sure I look at it. But have you seen it, or what would be a learning point for the listeners there?
Dr. Alison Schram: Exactly. And they usually do not. They usually do not explicitly say, “This looks like biallelic loss,” on the reports. The exception would be if there's a deep deletion, then that implies both copies of the gene have been deleted, and so then you can assume that it's a biallelic loss. But oftentimes, when you see a frameshift alteration or a mutation, you don't know whether or not it's a biallelic loss. And you may be able to get some clues based on the variant allele frequencies, but due to things like whole genome duplication or more complex tumor genomics, it's not clear from these reports, and you really do need a more in-depth bioinformatic analysis to understand whether these are biallelic or not. So that is why I suggest that this really needs to be done in the context of a clinical trial, but there is definitely a theoretical rationale for reporting and treating patients with biallelic losses perhaps more so than someone who has a variant of unknown significance that seems to be monoallelic.
The other tricky part, as I mentioned, is the fact that there could be epigenetic changes that silence the second copy, so that wouldn't be necessarily evident on a DNA report, and you would need more complex molecular testing to understand that as well.
Dr. Rafeh Naqash: Sure. Now, going to your study, could you tell us what prompted the study, what was the patient population that you collected, and how did you go about this research study design?
Dr. Alison Schram: It's actually a great story. I was the principal investigator for a clinical trial enrolling patients regardless of their tumor type to a combination of a PARP inhibitor and immunotherapy. And this was a large clinical trial that was being done as a basket study, as I mentioned, for patients that have either germline or somatic alterations with advanced solid tumors that had progressed on standard therapy. And the hypothesis was that the combination of a PARP inhibitor and immunotherapy would be synergistic and that there would be increased efficacy compared to either agent alone and that patients who had BRCA alterations were a sensitive population to test because of their inherent sensitivity to PARP inhibitors and perhaps their increased neoantigen burden from having loss of DNA repair.
So this large study, it's been published, really did show that there was efficacy across several tumor types, but it didn't seem to clearly demonstrate synergy between the immunotherapy and the PARP inhibitor as compared to what you might expect from a PARP inhibitor alone, and in addition to a couple of cases, perhaps attributable to the immunotherapy. So maybe additive rather than synergistic efficacy.
However, what really struck me looking at the data was that there were three patients with uterine leiomyosarcoma with BRCA deletions who had the best responses of anyone on the study. So incredible, durable responses. One of my patients with a complete response that continues to not have any evidence of cancer eight years after the initiation of this regimen. And for those of us that treat uterine leiomyosarcoma, this is unheard of. These patients generally, as I mentioned, respond, if they do respond to chemotherapy, it's generally short-lived and the cancer progresses. And so a complete response nearly a decade later turns heads in this field.
The other interesting thing was that these uterine leiomyosarcoma patients had somatic alterations rather than a germline alteration with a second hit, and the diseases that are best validated for being responsive to PARP inhibitors include the BRCA-associated diseases, the ones that you're at increased risk for if you have a germline BRCA mutation, including breast, pancreas, prostate, and ovarian. And so it was very interesting that this disease type that seemed to be uniquely sensitive to PARP inhibitors with immunotherapy was also different in that patients with uterine leiomyosarcoma don't tend to have a high frequency of BRCA alterations, and in patients that are born with a BRCA alteration, there doesn't seem to be a clearly increased risk of uterine sarcomas. So this population really jumped out as a uniquely sensitive population that differed from the prior indications for PARP inhibitors.
Given this patient and these couple of patients that we observed on the combination, in addition to some other case reports and case series that had started to come out in small numbers, we wanted to look back at our large cohort of patients at Memorial Sloan Kettering to see if we could really get a better sense of the numbers. How many patients at Sloan Kettering with uterine sarcomas have BRCA alterations? Are they generally somatic or germline? Are there unique features about these patients in terms of their clinical characteristics? How many of them have received PARP inhibitors, and if so, is this just luck that these three patients did so well, or is this really a good treatment option for patients with BRCA-altered uterine sarcomas? And so we did this retrospective analysis identifying the patients at Sloan Kettering who met these criteria.
So in total, we found 35 patients with uterine sarcomas harboring BRCA alterations, and the majority were leiomyosarcoma, about 86% of them had leiomyosarcoma, which is interesting because there are other uterine sarcomas, but it does seem like BRCA alterations tend to be more often in the leiomyosarcomas. And 13 of these patients with uterine leiomyosarcoma were treated with PARP inhibitors in the recurrent or metastatic setting with about half of those patients having an overall response, so that's a significant tumor shrinkage that sustained, and a clinical benefit rate of 62%. And if we look at the patients that had these BRCA2 deep deletions, which was the patient I had that had this amazing response, the overall response rate jumped to 60% and the clinical benefit rate to 80%. And we defined clinical benefit rate as having maintained on the PARP inhibitor without evidence of progression at six months. So this is really impressive for patients with a difficult to treat disease. And we couldn't do a randomized controlled trial comparing it to chemotherapy, but looking retrospectively at outcomes on chemotherapy studies, this was very favorable, particularly because many of these patients were heavily pretreated.
So to get a sense of, you know, how this might compare to chemotherapy, we tried to use patients as their own internal controls, and we looked at how long patients were maintained on the PARP inhibitor as compared to how long they were on the treatment just prior. And we used a ratio of 1.3 to say if they were on the PARP inhibitor for 1.3 times what their previous treatment was or longer, that is pretty clearly better, more of a benefit from that regimen. And the majority of patients did meet that bar. So 58% had a PFS ratio greater than 1.3, and the average PFS ratio was 1.9, suggesting, you know, you would expect the the later lines of therapy to actually not work as well, but this suggests that it's actually working better than the immediately prior line of therapy, to me, suggesting that this is truly a good treatment option for these patients.
Dr. Rafeh Naqash: Very interesting. And you mentioned that individuals with tumors having deep deletions were probably more responsive. How did you figure out that there was biallelic loss or deep deletions? Was that part of an extended analysis that was done subsequently?
Dr. Alison Schram: So the deletions reported on our report, if it's a biallelic deletion, that is the one biallelic molecular alteration that would be reported. So those are, by definition, biallelic, and I think that that may be one of the reasons that's a good biomarker. But also, what's interesting is that if you have both copies deleted of BRCA, you can't develop reversion mutations. So one of the the known mechanisms of resistance to PARP inhibitors in patients who have BRCA alterations are something called a reversion mutation where, if you have a frameshift alteration, for example, in BRCA that makes BRCA protein nonfunctional, you can develop a second mutation that actually puts the DNA back in frame, and a functional protein is now made. And so a mechanism of resistance to PARP inhibitors is actually reverting BRCA to a wild-type protein, and then BRCA's synthetic lethality no longer makes sense and is no longer effective. But if you've deleted both copies of BRCA, you don't have the ability to restore the function, and you can't develop reversion mutations. And that's perhaps why, you know, my patient and others have had these prolonged responses to PARP inhibitors because you don't have the same ability to develop that mechanism of resistance.
Dr. Rafeh Naqash: I remember thinking a year and a half back, I had an individual with prostate cancer and with BRCA2, and using liquid biopsy, I had a reversion mutation that we caught. In your practice, have you seen the utility of doing the serial liquid biopsies in these individuals to catch these reversion mutations?
Dr. Alison Schram: Yes, absolutely. And in patients that have the ability to develop a reversion mutation, serial cell-free DNA can catch it, but the caveat is that it doesn't always. So if you see an acquired reversion mutation in cell-free DNA, that can be helpful, particularly if you're planning on putting the patient on another line of therapy that might require a dysfunctional BRCA. So if you're putting them on a clinical trial with a PARP combination and the rationale is that they're sensitive because they don't have a functional BRCA, you would want to know if they developed a reversion mutation, and serial cell-free DNA can definitely identify these reversion mutations. Some of the major clinical trials in ovarian cancer have done serial cell-free DNA and have demonstrated the utility of that approach.
The caveat is that some of these reversion mutations are not readily caught on cell-free DNA because they're more complex reversion mutations, or they're not, the part of the gene that develops the reversion mutation is not tiled on the panel. And so it doesn't always catch the reversion mutations. Also, depends on the cell-free DNA shedding, depends on the tumor volume and other factors. And we published a related paper of a patient, it was a really interesting case of a patient with prostate cancer who was on a PARP inhibitor and developed what appeared to be a single reversion mutation on one sample, had negative cell-free DNA, single reversion mutation in a tissue biopsy, and then developed disease progression. And we did an autopsy, and the patient kindly consented to an autopsy, and at the time of autopsy, there were 10 unique reversion mutations identified across 11 metastases. So almost each metastasis had a unique reversion mutation, and only one of them had been seen premortem on a tissue biopsy and not on a cell-free DNA. But that autopsy really drove home to me how much we're missing by doing clinical testing in real time and we really don't know the entire genomic complexity of our patients by doing single samples. And theoretically, cell-free DNA can catch DNA from all the metastases, so you might think that that would be a solution, and it definitely can catch reversion mutations that are not seen in a single biopsy, but you really need to do it all. I mean, you need to do the tissue biopsy sampling, you need to do cell-free DNA, and probably one cell-free DNA test is not enough.
Dr. Rafeh Naqash: Thank you, again, for that very nice explanation.
Now, one quick provocative question. I remember when I was training, the lab that I used to work in, they used to do a lot of phosphorylation markers for DNA damage response, like phospho NBS, RAD51. Have you seen anything of that sort on these biallelic BRCA mutations where tumors are responding, but they also have a very high signature on the phosphorylation side, and it may or may not necessarily correspond to HRD signatures, but have you noticed or done any of that analysis?
Dr. Alison Schram: I think that it would be great to do that analysis. And some of the work we're doing now is actually trying to dig a little bit deeper in our cohort of patients to understand are these HRD-positive tumors? Does HRD positivity correlate with response to BRCA alterations? In terms of the functional assays, I would love to be able to do a functional assay in these samples.
One of the challenges is that this was a retrospective study and many of the patients were previously treated as standard of care or off-label with these agents, and so we didn't have prospective tissue collection, and so we're really limited by the tissue that was collected as part of standard of care and the consent forms that the patient signed that allow us to do genomic and molecular testing on their samples. So, I think that is hopefully future work that we will do and others will do.
Dr. Rafeh Naqash: Sure.
Shifting gears to your career trajectory, I'd like to spend a couple of minutes there before we end the podcast. So Dr. Schram, you've obviously been a trailblazer in this space of drug development, early-phase trials. Can you give us a brief synopsis of your journey and how you've successfully done what you're doing and what are some of the things that drive you?
Dr. Alison Schram: Well, thank you for saying that. I don't know if that's true, but I'll take the bait. I've been interested in oncology since college and was always very interested in not only the science of oncology but of course, treating patients. And in medical school, I did basic science research in a laboratory and it was very inspiring and made me want to do research in oncology in addition to clinical care. When I became an oncology fellow, I was presented with a very difficult question, which is, “Do you want to be a lab PI and be in the lab, or do you want to do clinical care and clinical research?” And I couldn't choose. I found a mentor who thankfully really had this amazing vision of combining the two and doing very early drug development, taking the data that was being generated by labs and translating it into patients at the earliest stage. So, you know, phase one drug development in molecularly targeted therapies. And so I became very interested as a fellow in early drug development and this ability to translate brand new molecular insights into novel drugs.
And I joined the- at Sloan Kettering, there was the Early Drug Development, it was actually a clinic, it was called something different, and it was very fortuitous. My last year of fellowship, the clinic became its own service with the ability to hire staff at Sloan Kettering, and I was the first ever hire to our Early Drug Development Service. And that really inspired me to try and bring these drugs to patients and to really translate the amazing molecular insights that my colleagues here at Sloan Kettering are discovering, and you know, of course, at other institutions and in pharma. And you know, there 's been an amazing revolution in in drug development over the last several years, and I feel very grateful that I've been here for it. You know, I've been able to take the brilliant insights from my colleagues and put these drugs in patients, and I have the amazing privilege of watching patients in many cases that benefit from these treatments. And so I do mostly phase one drug development and molecularly targeted therapies, and truthfully, I am just very fortunate to be around such brilliant people and to have both patients and labs trust me to be able to deliver these new drugs to patients and hopefully develop better drugs that move forward through FDA approval and reach patients across the country.
Dr. Rafeh Naqash: Thank you so much. That was very nicely put. And hopefully our trainees and junior faculty find that useful based on their own career trajectories.
Thank you, Dr. Schram, for joining us today. Hopefully, we'll see more of your subsequent work in JCO PO. Thank you for giving us all these insights today.
Dr. Alison Schram: Thank you for having me.
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 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.
Dr. Alison Schram Disclosures
Consulting or Advisory Role Company: Mersana, Merus NV, Relay Therapeutics, Schrodinger, PMV Pharma ,Blueprint Medicines, Flagship Pioneering, Redona Therapeutics, Repare Therapeutics, Endeavor BioMedicines
Research Funding Company: Recipient: Your Institution Merus, Kura, Surface Oncology, AstraZeneca, Lilly, Pfizer , Black Diamond Therapeutics, BeiGene, Relay Therapeutics, Revolution Medicines, Repare Therapeutics, PMV Pharma, Elevation Oncology, Boehringer Ingelheim
Travel, Accommodations, Expenses Company: PMV Pharma
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