Phase I Trial of Ipatasertib Plus Carboplatin, Carboplatin/Paclitaxel, or Capecitabine and Atezolizumab in Metastatic Triple-Negative Breast Cancer

Background: This trial evaluated the safety and efficacy of ipatasertib in combination with carboplatin, carboplatin/paclitaxel, or capecitabine/ atezolizumab in patients with metastatic triple-negative breast cancer (mTNBC). Methods: Eligibility criteria were mTNBC, RECIST 1.1 measurable disease, no prior use of platinum for metastatic disease (Arms A and B), and no prior exposure to immune checkpoint inhibitor (Arm C). Primary endpoints were safety and RP2D. Secondary endpoints were progression-free survival (PFS), response rate, and overall survival. Results: RP2D for Arm A (n = 10) was ipatasertib 300 mg daily, carboplatin AUC2, and paclitaxel 80 mg m(-2) days 1, 8, and 15 every 28 days. RP2D for Arm B (n = 12) was ipatasertib 400 mg daily and carboplatin AUC2 days 1, 8, and 15 every 28 days. RP2D for Arm C (n = 6) was likely ipatasertib 300 mg 21 days on 7 days off, capecitabine 750 mg m-2, twice a day, 7 days on 7 days off, and atezolizumab 840 mg days 1 and 15 every 28 days. The most common (>= 10%) grade 3-4 AEs at RP2D for Arm A (N = 7 at RP2D) were neutropenia (29%), diarrhea (14%), oral mucositis (14%), and neuropathy (14%); Arm B had diarrhea (17%) and lymphopenia (25%); and Arm C had anemia, fatigue, cognitive disturbance, and maculopapular rash (17% each). Overall responses at RP2D were 29% Arm A, 25% Arm B, and 33% Arm C. PFS was 4.8, 3.9, and 8.2 months for patients on Arms A, B, and C, respectively. Conclusions: Continuous dosing of ipatasertib with chemotherapy was safe and well-tolerated. Further study is warranted in understanding the role of AKT inhibition in treatment of TNBCs.