Ipatasertib plus Paclitaxel for Patients with PIK3CA/AKT1/PTEN-Altered Locally Advanced Unresectable or Metastatic Triple-Negative Breast Cancer in the IPATunity130 Phase III Trial.

Purpose: In the randomized phase II LOTUS trial, combining ipatasertib with first-line paclitaxel for triple-negative breast cancer (TNBC) improved progression-free survival (PFS), particularly in patients with PIK3CA/AKT1/PTEN-altered tumors. We aimed to validate these findings in a biomarker-selected TNBC population.

Patients And Methods: In Cohort A of the randomized double-blind placebo-controlled phase III IPATunity130 trial, taxane-eligible patients with PIK3CA/AKT1/PTEN-altered measurable advanced TNBC and no prior chemotherapy for advanced disease were randomized 2:1 to ipatasertib (400 mg, days 1-21) or placebo, both plus paclitaxel (80 mg/m2, days 1, 8, and 15), every 28 days until disease progression or unacceptable toxicity. The primary endpoint was investigator-assessed PFS.

Results: Between February 2018 and April 2020, 255 patients were randomized (168 to ipatasertib, 87 to placebo). At the primary analysis, there was no significant difference between treatment arms in PFS [hazard ratio 1.02, 95% confidence interval (CI), 0.71-1.45; median 7.4 months with ipatasertib vs. 6.1 months with placebo]. The final analysis showed no difference in overall survival between treatment arms (hazard ratio 1.08, 95% CI, 0.73-1.58; median 24.4 vs. 24.9 months, respectively). Ipatasertib was associated with more grade ≥3 diarrhea (9% vs. 2%) and adverse events leading to dose reduction (39% vs. 14%) but similar incidences of grade ≥3 adverse events (51% vs. 46%). Exploratory subgroup analyses by PAM50 and Burstein gene expression showed inconsistent results.

Conclusions: Adding ipatasertib to paclitaxel did not improve efficacy in PIK3CA/AKT1/PTEN-altered advanced TNBC. Biomarkers for benefit from PI3K/AKT pathway inhibition in TNBC remain poorly understood.