Dr. Angela DeMichele, Dr. Lynn Henry, and Dr. Harold Burstein present the latest breast cancer rapid recommendation update impacting two ASCO guidelines. This update focuses on the new option, capivasertib plus fulvestrant, for patients with hormone receptor-positive, HER2-negative metastatic breast cancer with activating PIK3CA or AKT1 mutations or inactivating alterations in PTEN based on data from the recent CAPItello-291 trial. They discuss the updated recommendations on lines of endocrine treatment and selecting between the options for patients with activating PIK3CA mutations. Additionally, we discuss implications for clinicians and patients, and what ongoing research is occurring in the field. Read the latest update, “Endocrine and Targeted Therapy for Hormone Receptor-Positive, HER2-Negative Metastatic Breast Cancer – Capivasertib-Fulvestrant: ASCO Rapid Guideline Update“ at www.asco.org/breast-cancer-guidelines. TRANSCRIPT This guideline, clinical tools, and resources are available at www.asco.org/breast-cancer-guidelines. Read the full text of the guideline and review authors’ disclosures of potential conflicts of interest in the Journal of Clinical Oncology, https://ascopubs.org/doi/10.1200/JCO.24.00248 Brittany Harvey: Hello, and welcome to the ASCO Guidelines podcast, one of ASCO's podcasts delivering timely information to keep you up to date on the latest changes, challenges, and advances in oncology. You can find all the shows, including this one, at asco.org/podcasts.   My name is Brittany Harvey, and today I am interviewing Dr. Harold Burstein from Dana-Farber Cancer Institute, Dr. Angela DeMichele from the University of Pennsylvania, and Dr. Lynn Henry from the University of Michigan, co-chairs on “Endocrine and Targeted Therapy for Hormone Receptor-Positive, HER2-Negative Metastatic Breast Cancer: Capivasertib–Fulvestrant: ASCO Rapid Guideline Update.” Thank you for being here, Dr. Burstein, Dr. DeMichele, and Dr. Henry. Dr. Harold Burstein: We're happy to be here.  Brittany Harvey: And before we discuss this guideline, I'd like to note that ASCO takes great care in the development of its guidelines and ensuring that the ASCO conflict of interest policy is followed for each guideline. The disclosures of potential conflicts of interest for the guideline panel, including our guests on this episode today, are available online with the publication of the guideline update in the Journal of Clinical Oncology, which is linked in the show notes.  So then, to kick us off, Dr. Burstein, could you first describe what prompted this rapid update, which provides updated recommendations for two ASCO guidelines: the biomarkers for systemic therapy in metastatic breast cancer guideline, and the endocrine treatment and targeted therapy for hormone receptor-positive, HER2-negative metastatic breast cancer guideline? Dr. Harold Burstein: Thanks, Brittany. Well, this team has been working, as you mentioned, actually, on two guidelines, which are clearly evolving in parallel and kind of converging, actually, when you look at data, as we'll be talking about in the next few minutes. The particular catalyst here was a large randomized clinical trial which looked at a new targeted therapy in the space of estrogen receptor-positive, HER2-negative breast cancer. That drug is capivasertib. And the trial was the so-called CAPItello study. In that trial, patients who were receiving second-line therapy with fulvestrant were randomized to that treatment alone, or that plus capivasertib. So the data from that study were the first strong signal that we needed to update the guideline because they were important clinical data.   The other strong signal was that the drug was tested in a cohort of patients who had a specific set of mutations in their cancers. And that included PIK3CA mutations, a class of mutations for which we already had a targeted drug. But it also included some new potential targets