Toxicity Attribution in PIK3CA-Mutated HR+/HER2-Negative Advanced Breast Cancer

Dr. Jason Mouabbi discusses how to approach adverse-event attribution when treating patients with PIK3CA-mutated HR-positive/HER2-negative advanced breast cancer with a multidrug regimen. He reviews the distinct toxicity profiles associated with inavolisib, palbociclib, and fulvestrant, noting that hyperglycemia, rash, diarrhea, and stomatitis are key toxicities associated with inavolisib, while neutropenia is an important consideration with palbociclib and injection-site reactions may occur with fulvestrant. Dr. Mouabbi explains how recognizing the characteristic toxicity profile of each treatment component can help clinicians identify the most likely cause of an adverse event and determine the appropriate management approach. He emphasizes grading toxicities using established criteria as an important step in deciding whether treatment should be continued, temporarily held, dose reduced, or discontinued. The discussion highlights the importance of evaluating toxicity severity and recurrence when making treatment modifications while maintaining an individualized approach to adverse-event management.