Gedatolisib Combined with Palbociclib and Letrozole in Patients with No Prior Systemic Therapy for Hormone...

Nonclinical evidence demonstrating that estrogen receptor, cyclin-dependent kinases 4 and 6 (CDK4/6), and PI3K/AKT/mTOR (PAM) pathways cross-promote tumor proliferation in hormone receptor-positive (HR+)/HER2- breast cancer cell lines led to the development of CDK4/6 inhibitors and agents inhibiting single PAM pathway nodes to treat HR+/HER2- advanced breast cancer. Simultaneous blockade of the estrogen receptor, CDK4/6, and PAM pathways may optimize antitumor control in the treatment-naïve advanced breast cancer setting. Gedatolisib, a pan-PI3K/mTOR inhibitor, was evaluated as first-line therapy, combined with standard-of-care palbociclib and letrozole, for patients with HR+/HER2- advanced breast cancer.

Treatment-naïve patients from a phase Ib study with HR+/HER2- advanced breast cancer treated with gedatolisib plus palbociclib and letrozole were analyzed. The primary endpoint of the overall study was investigator-assessed objective response. Secondary endpoints included safety, duration of response, progression-free survival (PFS), and overall survival.

Of 41 patients, all had stage IV disease, 93% had measurable disease, 78% had visceral metastases, and 22% had detectable PIK3CA mutations. The objective response rate was 79% in patients with evaluable disease (N = 33). The median duration of response was 48 months for confirmed responders. The median PFS was 48.4 months, and the median overall survival was 77.3 months. The overall response rate and PFS were comparable in patients with and without PIK3CA mutations. Fewer than 10% discontinued treatment due to treatment-related adverse events. The most frequent grade 3/4 adverse events were neutropenia (61%), rash (39%), and oral stomatitis (29%).

Gedatolisib plus palbociclib and letrozole demonstrated preliminary efficacy in patients with no prior systemic therapy for advanced breast cancer. These results warrant further evaluation of gedatolisib added to standard-of-care, first-line therapy for HR+/HER2- advanced breast cancer.