Background: Chemotherapy treatments with robust efficacy that preserve quality of life are needed. T is a novel, oral taxane that has potential advantages over currently available taxanes, including: oral administration with a low pill burden and once every 3 week (Q3W) dosing; no observed hypersensitivity reactions; preclinical evidence of central nervous system (CNS) penetration; and improved activity against chemotherapy-resistant tumors. More than 600 pts have been treated with T in clinical studies. T had robust monotherapy activity in a P2 study in 38 pts with HER2-, HR+ MBC, with a confirmed objective response rate (ORR) per RECIST 1.1 of 45%. Methods: CONTESSA TRIO is a 2-cohort, multinational, multicenter, P2 study. In Cohort 1, 90 pts (potential expansion to up to 150 pts) with metastatic TNBC who have not received prior chemotherapy for advanced disease will be randomized 1:1:1 to receive T at 27 mg/m² Q3W plus either: (1) nivolumab at 360 mg Q3W; (2) pembrolizumab at 200 mg Q3W; or (3) atezolizumab at 1,200 mg Q3W. Nivolumab and pembrolizumab (PD-1 inhibitors) and atezolizumab (a PD-L1 inhibitor) are approved for the treatment of multiple types of cancer; atezolizumab, in combination with nab-paclitaxel, was recently approved in the US for the treatment of metastatic TNBC. The dual primary endpoints for Cohort 1 are ORR and progression-free survival (PFS). A sample size of 30 pts in each PD-(L)1 inhibitor treatment group has approximately 70% power to detect an ORR difference of ≥ 35% between the treatment group with the highest ORR and the treatment group with the lowest ORR. Secondary endpoints include duration of response (DoR) and overall survival (OS). Efficacy results for each of the 3 PD-(L)1 inhibitor combinations will be assessed for correlation with the results of each of the 3 approved PD-L1 diagnostic assays. CONTESSA TRIO is the first randomized clinical study to compare 3 approved PD-(L)1 inhibitors. In Cohort 2, 40 elderly pts (potential expansion to up to 60 pts) with HER2- MBC who have not received prior chemotherapy for advanced disease will receive T monotherapy at 27 mg/m² Q3W. The primary endpoint for Cohort 2 is ORR. A sample size of 40 will allow the ORR to be estimated with a maximum standard error of < 8%. Secondary endpoints include PFS, DoR and OS. Pts with CNS metastases are eligible for both cohorts. The study was initiated in March 2019. Clinical trial information: NCT03952325.