A Study to Evaluate the Safety and Tolerability of TOS-358 in Adults With HR+ Breast Cancer and Other Select Solid Tumors

Description

This study will be conducted in two parts: a dose finding portion to determine the maximum tolerated dose and recommended phase 2 dose (RP2D) of TOS-358 administered orally on once a day (QD) and twice daily (BID) schedules, and a dose expansion portion to evaluate safety and tolerability in tumor-specific cohorts administered TOS-358 at the recommended phase 2 dose and schedule.

Adult subjects with histologically confirmed diagnosis of hormone receptor-positive (HR+), human epidermal growth factor receptor 2 (HER2) negative breast cancer, squamous cell carcinoma of the head and neck, cancer of the bladder, or endometrial cancer with known PIK3CA mutations or amplifications and who meet all of the eligibility criteria will be enrolled in the study.

In the dose finding portion of the study, TOS-358 will be evaluated as a single-agent at multiple dose levels administered orally until disease progression, unacceptable toxicity, or until meeting any other reason for discontinuation as specified in the protocol.