Inavolisib-Based Therapy in PIK3CA-Mutated Advanced Breast Cancer.

Background: Inavolisib is a highly potent and selective inhibitor of the alpha isoform of the p110 catalytic subunit of the phosphatidylinositol 3-kinase complex (encoded by PIK3CA) that also promotes the degradation of mutated p110α. Inavolisib plus palbociclib-fulvestrant has shown synergistic activity in preclinical models and promising antitumor activity in early-phase trials.

Methods: In a phase 3, double-blind, randomized trial, we compared first-line inavolisib (at an oral dose of 9 mg once daily) plus palbociclib-fulvestrant (inavolisib group) with placebo plus palbociclib-fulvestrant (placebo group) in patients with PIK3CA-mutated, hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative locally advanced or metastatic breast cancer who had had relapse during or within 12 months after the completion of adjuvant endocrine therapy. The primary end point was progression-free survival as assessed by the investigator.

Results: A total of 161 patients were assigned to the inavolisib group and 164 to the placebo group; the median follow-up was 21.3 months and 21.5 months, respectively. The median progression-free survival was 15.0 months (95% confidence interval [CI], 11.3 to 20.5) in the inavolisib group and 7.3 months (95% CI, 5.6 to 9.3) in the placebo group (hazard ratio for disease progression or death, 0.43; 95% CI, 0.32 to 0.59; P<0.001). An objective response occurred in 58.4% of the patients in the inavolisib group and in 25.0% of those in the placebo group. The incidence of grade 3 or 4 neutropenia was 80.2% in the inavolisib group and 78.4% in the placebo group; grade 3 or 4 hyperglycemia, 5.6% and 0%, respectively; grade 3 or 4 stomatitis or mucosal inflammation, 5.6% and 0%; and grade 3 or 4 diarrhea, 3.7% and 0%. No grade 3 or 4 rash was observed. Discontinuation of any trial agent because of adverse events occurred in 6.8% of the patients in the inavolisib group and in 0.6% of those in the placebo group.

Conclusions: In patients with PIK3CA-mutated, hormone receptor-positive, HER2-negative locally advanced or metastatic breast cancer, inavolisib plus palbociclib-fulvestrant led to significantly longer progression-free survival than placebo plus palbociclib-fulvestrant, with a greater incidence of toxic effects. The percentage of patients who discontinued any trial agent because of adverse events was low. (Funded by F. Hoffmann-La Roche; INAVO120 ClinicalTrials.gov number, NCT04191499.).