Co-Mutations Complicate ESR1-Directed Treatment Decisions

Carol Tweed, MD, and Neil Iyengar, MD, discuss how co-occurring mutations such as PIK3CA, AKT1, and TP53 complicate treatment decisions once an ESR1 mutation emerges in hormone receptor-positive, HER2-negative metastatic breast cancer. Dr. Tweed notes that newer oral agents targeting PI3 kinase are effective but not durable, and that adding a co-medication like capivasertib introduces additional toxicity even when symptomatic response can be robust. Dr. Iyengar explains that despite these co-mutations, oral selective estrogen receptor degraders retain activity across the molecular landscape, though PIK3CA and AKT1 alterations still portend a worse prognosis. He describes combining an AKT inhibitor with a selective estrogen receptor degrader as biologically attractive but says the decision depends on how much additional symptom burden a patient can tolerate, with transparency about durability of response central to that conversation.