Dr. Allison Zibelli and Dr. Megan Kruse discuss the potential benefit of endocrine therapy in ER-low breast cancer; the efficacy and tolerability of triplet therapy in PIK3CA-mutated, HER2-negative locally advanced or metastatic breast cancer; and more key research that will be featured 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 today. I am an associate professor of medicine and a breast medical oncologist at the Sidney Kimmel Cancer Center of Jefferson Health in Philadelphia. My guest today is Dr. Megan Kruse, a breast medical oncologist and director of breast cancer research at the Cleveland Clinic Taussig Cancer Institute. We'll be discussing key abstracts in breast cancer that will be featured at the 2024 ASCO Annual Meeting.  Our full disclosures are available in the transcript of this episode, and disclosures related to all episodes of the podcast are available at asco.org/DNpod.  Megan, it's great to have you back on the podcast. Dr. Megan Kruse: Thanks, Alison. Happy to be here. Dr. Allison Zibelli: So, let's begin with Abstract 505. This was another analysis of the SWOG S1007 (RxPONDER) trial, which was the trial that was looking at premenopausal women with intermediate risk oncotype scores. And do they benefit from chemotherapy? If you analyze the whole group, they do benefit from chemotherapy, but what this study questions is whether we can pull out the subset of these patients that actually benefit from chemotherapy? And what they tried doing was measuring various endocrine reproductive hormones and found that anti-mullerian hormone over 10 was the only one that predicted for chemotherapy benefit. What are your key takeaways from this study? Will it help us figure out who is truly postmenopausal biochemically? Dr. Megan Kruse: I think this is really promising. This is one of the toughest situations in clinic, honestly, when you have a premenopausal woman who has an intermediate oncotype risk. We know that chemotherapy is not going to make a huge difference potentially in their breast cancer outcomes, but it may add to some small differential benefit. I think that many of our patients are really afraid about leaving any impactful therapy on the table. And so, it'd be nice to have another marker to help sort out who in this group will really benefit. And the AMH levels, I think, are something that are very accessible for most practices, easily orderable. And it seems like this cutoff of 10 is a very well-known cut point in the AMH interpretation, and a pretty clear-cut point. So, I think it gives a little bit more objective view of who may actually benefit or not.  When you look at the results shown in this abstract, for the women in the recurrence score less than 25 receiving chemotherapy followed by endocrine therapy, they had a benefit in five-year invasive disease-free survival of 7.8%. When you look at those oncotype reports and they suggest how much benefit you might get, that's right around the same number you see. So, I think that's supporting that this is the subgroup that's benefiting.  When you look at those patients with AMH less than 10, they actually had a negative 1.7% difference in overall survival. So, you wonder, are we harming these patients by giving them chemotherapy? I think that's too far of a stretch to say. I wouldn't be worried about harm. But hopefully, we can stop giving chemotherapy to patients who truly are not going to benefit if we have an additional biomarker of response. That's what the promise is for this.  So again, another potentially actionable abstract that we can put into practice pretty quickly. It’s going to be hard to know how to use this, also in the context of the upcoming OFSET study or BR009, which is of course the study in the same group of premenopausal patients with node-negative or 1-3 lymph nodes involved, and intermediate oncotype scores, randomizing them to end