Zovegalisib & PIK3CA+ Breast Cancer: Promising Results

The landscape of treatment for PIK3CA-mutated, hormone receptor-positive/HER2-negative advanced breast cancer is shifting, with new data presented at the 2025 San Antonio Breast Cancer Symposium (SABCS) demonstrating promising efficacy for the combination of zovegalisib, a PI3Kα inhibitor, and fulvestrant. This is particularly significant as these patients often face limited options after progressing on CDK4/6 inhibitors – a common first-line treatment. The ReDiscover trial results signal a potential new standard of care for a substantial subset of breast cancer patients, addressing a critical unmet need.

The rationale behind combining a PI3Kα inhibitor like zovegalisib with fulvestrant stems from the understanding that PIK3CA mutations are key drivers of hormone receptor-positive breast cancer. Approximately 40% of HR+/HER2- advanced breast cancers harbor a PIK3CA mutation. CDK4/6 inhibitors have significantly improved outcomes in this population, but resistance inevitably develops, creating a need for effective subsequent therapies. PI3Kα inhibition offers a targeted approach to overcome this resistance, particularly in patients whose tumors are driven by this specific mutation. The trial’s focus on patients *after* CDK4/6 inhibitor failure is crucial; it addresses a real-world clinical scenario where treatment options are dwindling.

The observed efficacy differences based on ESR1 mutation status and prior SERD exposure are also noteworthy. ESR1 mutations are frequently acquired after treatment with endocrine therapies, contributing to resistance. The higher response rate in the ESR1-mutated population suggests that PI3Kα inhibition may be particularly effective in overcoming this resistance mechanism. Similarly, prior SERD exposure didn’t negate the benefit, indicating the combination could be valuable even for patients who’ve exhausted other endocrine-based options.

The Forward Look

While these phase 1 results are encouraging, the next critical step is the ongoing phase 3 CONFIRM trial (NCT05968469), which will compare zovegalisib plus fulvestrant to standard-of-care endocrine therapy in a larger patient population. Positive results from CONFIRM will likely pave the way for regulatory submissions and potential approval, establishing zovegalisib as a new standard of care in this setting. Beyond regulatory approval, we can anticipate increased focus on comprehensive genomic profiling to identify patients with PIK3CA mutations who are most likely to benefit from this targeted therapy. Furthermore, research will likely expand to explore combinations of zovegalisib with other targeted agents or immunotherapies to further enhance efficacy and overcome potential resistance mechanisms. The relatively benign safety profile observed in the ReDiscover trial – with no grade 4 treatment-related adverse events – is also a positive indicator for broader clinical adoption. The field is moving towards precision oncology, and this data reinforces the importance of identifying actionable mutations like PIK3CA to guide treatment decisions and improve outcomes for patients with advanced breast cancer.

1. Saura C, Curigliano G, Italiano A, et al. Efficacy of mutant-selective PI3Kα inhibitor RLY-2608 in combination with fulvestrant in patient (pt) subset populations, including pts with PIK3CA-mutant HR+/HER2- advanced breast cancer (BC) pre-treated with fulvestrant or other SERD. Presented at: 2025 San Antonio Breast Cancer Symposium; December 9-12, 2025; San Antonio, TX. Abstract 799
2. First-in-human study of mutant-selective PI3Kα Inhibitor, RLY-2608, as a single agent in patients with advanced solid tumors and in combination with endocrine therapy +/​- a CDK4/​6 or CDK4 inhibitor in patients with advanced solid tumors or advanced breast cancer. ClinicalTrials.gov. Updated September 22, 2025. Accessed December 23, 2025. https://tinyurl.com/2hjy6znt