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.

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