Leading breast cancer expert Dr. Virginia Borges has provided crucial insights into the evolving treatment landscape for hormone receptor-positive, HER2-negative metastatic breast cancer, particularly focusing on the promising role of capivasertib in patients with PIK3CA mutations.
Breakthrough Results from CAPItello-291 Trial
The phase 3 CAPItello-291 trial has established capivasertib's efficacy in combination with fulvestrant for patients with hormone receptor-positive advanced breast cancer. The study, which enrolled 708 patients, demonstrated remarkable results in the AKT pathway-altered population, with median progression-free survival reaching 7.3 months for the capivasertib group compared to 3.1 months in the placebo group (HR 0.50; 95% CI, 0.38-0.65; P < .001).
Importantly, the trial showed an overall survival benefit across all patients, with a hazard ratio of 0.74 (95% CI, 0.56-0.98), leading to FDA approval. The study included patients who had received up to two prior lines of endocrine therapy and one line of chemotherapy in the advanced setting, with 51% having previous CDK4/6 inhibitor exposure.
Treatment Selection and Clinical Considerations
Dr. Borges highlighted the advantages of capivasertib over alternative treatments, particularly alpelisib, for patients with PIK3CA mutations. "Capivasertib is an easier drug to give, with less rash and blood sugar elevation issues," noted Dr. Borges. The drug targets AKT, PTEN, and PI3 kinase mutations, offering broader therapeutic potential.
The dosing schedule requires careful management, following a 4-days-on, 3-days-off regimen. While blood sugar monitoring remains important, particularly for diabetic patients, the side effect profile appears more manageable compared to alpelisib.
Molecular Testing Strategy
For optimal treatment selection, Dr. Borges emphasizes the importance of timing molecular testing appropriately. She recommends testing for PIK3CA mutations before disease progression on current therapy, allowing for better treatment planning. The presence of both PIK3CA and ESR1 mutations would typically lead to prioritizing PIK3CA-targeted therapy due to its role as a driver mechanism.
Managing Side Effects and Monitoring
Patient monitoring includes regular complete blood count with differential and fasting biochemistry panels at follow-up visits. The most common side effect, diarrhea, can typically be managed with loperamide as needed. Treatment efficacy is monitored through imaging, with successful cases showing reduced avidity in osseous lesions on PET-CT scans.
Future Directions and Treatment Evolution
The landscape of breast cancer treatment continues to evolve, particularly regarding HER2 expression patterns. Dr. Borges notes that HER2 status can change from primary to metastatic disease, though significant shifts to HER2-positive are rare (2.4% from HER2-0 and 1.6% from HER2-low).
The emergence of new therapeutic options, including novel selective estrogen receptor degraders (SERDs) and modulators, suggests an expanding array of treatment possibilities for patients with hormone receptor-positive metastatic breast cancer. This evolving landscape emphasizes the importance of sequential molecular testing to guide treatment decisions throughout the disease course.
