DESTINY-Breast06 and A-BRAVE: Advances in Breast Cancer Research

Dr. Allison Zibelli and Dr. Erika Hamilton discuss the results of the DESTINY-Breast06 trial in HR+, HER2-low and HER2-ultralow metastatic breast cancer and the A-BRAVE trial in early triple-negative breast cancer, the results of which were both presented at the 2024 ASCO Annual Meeting.


TRANSCRIPT


Dr. Allison Zibelli: Hello, I'm Dr. Allison Zibelli, your guest host of the ASCO Daily News Podcast. I'm an associate professor of medicine and breast medical oncologist at the Sidney Kimmel Cancer Center of Jefferson Health in Philadelphia. My guest today is Dr. Erika Hamilton, a medical oncologist and director of breast cancer research at the Sarah Cannon Research Institute. We'll be discussing the DESTINY-Breast06 trial (https://meetings.asco.org/abstracts-p...) , which showed a progression-free advantage with the antibody-drug conjugate trastuzumab deruxtecan (T-DXd) compared to chemotherapy in hormone receptor-positive HER2-low or HER2-ultralow metastatic breast cancer. We'll address the implications of this study for the community, including the importance of expanding pathology assessments to include all established subgroups with HER2 expression, and the promise of expanding eligibility for antibody-drug conjugates. We'll also highlight advances in triple-negative breast cancer, focusing on the A-BRAVE trial (https://dailynews.ascopubs.org/do/a-b...) , the first study reporting data on an immune checkpoint inhibitor avelumab in patients with triple-negative breast cancer with invasive residual disease after neoadjuvant chemotherapy. 


Our full disclosures are available in the transcript of this episode. 


Erika, it's great to have you on the podcast today.


Dr. Erika Hamilton: Thanks so much, Allison. Happy to join.


Dr. Allison Zibelli: Antibody-drug conjugates are rapidly changing the treatment landscape in breast cancer. The data from the DESTINY-Breast06 trial suggests that trastuzumab deruxtecan may become a preferred first-line treatment option for most patients with HER2-low or HER2-ultralow metastatic breast cancer after progression on endocrine therapy. First, could you remind our listeners, what's the definition of HER2-ultralow and what were the findings of this trial?


Dr. Erika Hamilton: Yeah, those are fantastic questions. Ultralow really has never been talked about before. Ultralow is part of a subset of the IHC zeros. So it's those patients that have HER2-tumor staining that's less than 10% and incomplete but isn't absolutely zero. It's even below that +1 or +2 IHC that we have classified as HER2-low. Now, I think what's important to remember about D-B06, if you recall, D-B04 (DESTINY-Breast04 (https://dailynews.ascopubs.org/do/des...) ) was our trial looking at HER2-low, is that D-B06 now included HER2-low as well as this HER2-ultralow category that you asked about. And it also moved trastuzumab deruxtecan up into the frontline. If you recall, D-B04 was after 1 line of cytotoxic therapy. So now this is really after exhausting endocrine therapy before patients have received other chemotherapy.


And what we saw was an improvement in progression-free survival that was pretty significant: 13.2 months versus 8.1 months, it was a hazard ratio of 0.62. And you can ask yourself, “well, was it mainly those HER2-low patients that kind of drove that benefit? What about the ultralow category?” And when we look at ultralow, it was no different: 13.2 months versus 8.3 months, hazard ratio, again, highly significant. So I think it's really encouraging data and gives us some information about using this drug earlier for our patients with hormone receptor-positive but HER2-negative disease. 


Dr. Allison Zibelli: I thought this study was really interesting because it's a patient population that I find very difficult to treat, the hormone receptor-positive metastatic patient that's not responding to endocrine therapy anymore. But it's important to mention that T-DXd resulted in more serious toxicities compared to traditional chemotherapy in this study. So how do you choose which patients to offer this to?


Dr. Erika Hamilton: Yeah, those are both great points. So you're right, this is after endocrine therapy. And in fact, about 85% of these patients had received at least 2 prior lines of endocrine therapy. So I have some people kind of asking, “Well, if endocrine therapy really isn't benefiting everyone in the second-line setting post-CDK, should we just move to the ADCs?” And, no, probably we should really make sure that we're exhausting endocrine therapies for those patients that are going to benefit. And once we determine somebody has endocrine-resistant disease, that's when we would think about switching.


In terms of the side effects, I think you're right. It's mainly ILD that's probably the more seri...