In this JCO Article Insights episode, Giselle de Souza Carvalho provides a summary on " Navigating Treatment Pathways in Metastatic Hormone Receptor–Positive, HER2-Negative Breast Cancer: Optimizing Second-Line Endocrine and Targeted Therapies " by Bhardwarj, et al and " US Food and Drug Administration Approval Summary: Capivasertib With Fulvestrant for Hormone Receptor–Positive, Human Epidermal Growth Factor Receptor 2–Negative Locally Advanced or Metastatic Breast Cancer With PIK3CA/AKT1/PTEN Alterations " by Dilawari et al published in the Journal of Clinical Oncology. TRANSCRIPT Giselle Carvalho: Hello and welcome to JCO Article Insights episode for the December issue of the Journal of Clinical Oncology . I'm your host Giselle Carvalho, Medical Oncologist in Brazil focusing on breast cancer and melanoma skin cancers and one of the ASCO Editorial Fellows at JCO this year. Today, I will be discussing two articles. The first one is " Navigating Treatment Pathways in Metastatic Hormone Receptor–Positive, HER2-Negative Breast Cancer: Optimizing Second-Line Endocrine and Targeted Therapies ," and the second one is the " US FDA Approval Summary on Capivasertib with Fulvestrant for HR-positive HER2-negative Locally Advanced or Metastatic Breast Cancer with PIK3CA/AKT1/PTEN Alteration. " As we know, 65% to 70% of all breast cancers are HR-positive HER2-negative and this is also the most common subtype of metastatic breast cancer. The current standard of care for frontline therapy of patients with luminal metastatic disease is a CDK4/6 inhibitor in combination with endocrine therapy. However, as new endocrine and targeted therapies gain approval, choosing the best systemic therapy upon disease progression after frontline therapy is a topic of ongoing debate. Nearly 40 to 50% of HR-positive breast cancers have actionable genomic alterations and molecular testing should be a routine recommendation for patients with metastatic HR-positive HER2-negative disease. This can be performed repeating tissue biopsy at the time of progression or from archival tissue. Treatment options after progression on CDK4/6 inhibitors include alpelisib in combination with fulvestrant in patients with PIK3CA mutant tumors as seen in the SOLAR-1 trial, or capivasertib with fulvestrant in patients with a tumor mutation in (PI3K)–AKT–PTEN pathway as seen in the CAPItello-291 study, which will be discussed further. In approximately 30% of patients, progression on frontline endocrine plus CDK4/6 inhibitor treatment is caused by endocrine resistance, frequently involving activating mutations in ESR1. For those tumors, elacestrant, an oral SERD is an option as demonstrated in the EMERALD trial. For patients with a BRCA mutation, PARP inhibitors represent another option. If no mutations are detected, everolimus, an mTOR inhibitor, can be used based on the BOLERO-2 results. The phase 2 MAINTAIN and PACE trials, along with the phase 3 postMONARCH trial support changing the endocrine therapy backbone with or without switching the CDK4/6 inhibitor. In less resourced areas, fulvestrant monotherapy is still an option to delay cytotoxic chemotherapy, though its efficacy is limited when used as a single agent. Finally, after progression on at least one line of chemotherapy, antibody drug conjugates including sacituzumab govitecan or trastuzumab deruxtecan may be an option. Now focusing on the PI3K AKT PTEN signaling pathway, activating mutations in PIK3CA and AKT1 and inactivating alterations in PTEN occur in approximately half of luminal breast cancers. In June 2023, the CAPItello-291 trial was published and treatment with fulvestrant plus capivasertib, a PTEN AKT inhibitor, demonstrated a 3.6 month PFS benefit compared to fulvestrant alone, regardless of the presence of AKT pathway alterations. However, for those with tumors without AKT pathway alteration, an exploratory analysis showed that although there was a numerical improvement in PFS, it did not meet statistical significance, indicating that the biomarker positive population primarily drove the positive results noted in the overall population. Therefore, capivasertib plus fulvestrant was approved by the US FDA in November 2023 exclusively for patients with PI3K/AKT1/PTEN tumor alterations after progression on an aromatized inhibitor with or without a CDK4/6 inhibitor. The approved schedule of capivasertib is slightly different from that of other agents used in breast cancer. It is 400 milligrams taken orally twice a day for four days per week every week in a 28-day cycle in combination with fulvestrant. Diarrhea, rash and hyperglycemia were the most commonly reported grade three or four adverse events in the interventional group. I would like to highlight that even though the CAPItello trial excluded patients with glycosylated hemoglobin levels higher than 8% or those diagnosed with diabetes who required insulin, hyperglycemia occurred in 19% of biomarker positive patients treated with capivaser
