Breast Cancer Research Poised to Change Practice From ASCO25

Dr. Allison Zibelli and Dr. Rebecca Shatsky discuss advances in breast cancer research that were presented at the 2025 ASCO Annual Meeting, including a potential new standard of care for HER2+ breast cancer, the future of ER+ breast cancer management, and innovations in triple negative breast cancer therapy. Transcript Dr. Allison Zibelli: Hello and welcome to the ASCO Daily News Podcast. I'm Dr. Allison Zibelli, your guest host of the podcast today. I'm an associate professor of medicine and a breast medical oncologist at the Sidney Kimmel Comprehensive Cancer Center at Jefferson Health. There was a substantial amount of exciting breast cancer data presented at the 2025 ASCO Annual Meeting, and I'm delighted to be joined by Dr. Rebecca Shatsky today to discuss some of these key advancements. Dr. Shatsky is an associate professor of medicine at UC San Diego and the head of breast medical oncology at the UC San Diego Health Moores Cancer Center, where she also serves as the director of the Breast Cancer Clinical Trials Program and the Inflammatory and Triple-Negative Breast Cancer Program. Our full disclosures are available in the transcript of this episode. Dr. Shatsky, it's great to have you on the podcast today. Dr. Rebecca Shatsky: Thanks, Dr. Zibelli. It's wonderful to be here. Dr. Allison Zibelli: So, we're starting with DESTINY-Breast09, which was trastuzumab deruxtecan and pertuzumab versus our more standard regimen of taxane, trastuzumab pertuzumab for first-line treatment of metastatic HER2-positive breast cancer. Could you tell us a little bit about the study? Dr. Rebecca Shatsky: Yeah, absolutely. So, this was a long-awaited study. When T-DXd, or trastuzumab deruxtecan, really hit the market, a lot of these DESTINY-Breast trials were started around the same time. Now, this was a global, randomized, phase 3 study presented by Dr. Sara Tolaney from the Dana-Farber Cancer Institute of Harvard in Boston. It was assessing essentially T-DXd in the first-line setting for metastatic HER2-positive breast cancer in addition to pertuzumab. And that was randomized against our standard-of-care regimen, which was established over a decade ago by the CLEOPATRA trial, and we've all been using that internationally for at least the past 10 years. So, this was a large trial, and it was one-to-one-to-one of patients getting T-DXd plus pertuzumab, T-DXd alone, or THP, which mostly is used as docetaxel and trastuzumab and pertuzumab every three weeks for six cycles. And this was in over 1,000 patients; it was 1,159 patients with metastatic HER2-positive breast cancer. This was a very interesting trial. It was looking at the use of trastuzumab deruxtecan, but patients were started on this treatment for their first-line metastatic HER2-positive breast cancer with no end date to their T-DXd. So, it was, you know, you were started on T-DXd every 3 weeks until progression. Now, CLEOPATRA is a little bit different than that, though, as we know. So, CLEOPATRA has a taxane plus trastuzumab and pertuzumab. But generally, patients drop the taxane after about six to seven cycles because, as we know, you can't be really on a taxane indefinitely. You get pretty substantial neuropathy as well as cytopenias, other things that end up happening. And so, in general, that regimen has sort of a limited time course for its chemotherapy portion, and the patients maintained after the taxane is dropped on their trastuzumab and their pertuzumab, plus or minus endocrine therapy if the investigator so desires. And the primary endpoint of the trial was progression-free survival by blinded, independent central review (BICR) in the intent-to-treat population. And then it had its other endpoints as overall survival, investigator-assessed progression-free survival, objective response rates, and duration of response, and of course, safety. As far as the results of this trial, so, I think that most of us key opinion leaders in breast oncology were expecting