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 colorectal cancer, gastric cancer, non-small cell lung cancer, human epidermal growth factor receptor 2 (HER2) negative breast cancer, squamous cell carcinoma of the head and neck, urothelial cancer, or select gynecologic cancers (ovarian cancer, cervical cancer, or endometrial cancer) with known PIK3CA mutations or amplifications (as determined at a College of American Pathologists/clinical laboratory improvement amendments [CAP/CLIA]-certified or equivalently accredited diagnostic laboratory using a validated test), who meet all of the eligibility criteria will be enrolled in the Phase 1 portion of 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.
The goal of this clinical trial is to evaluate the safety of TOS-358 in adults with select solid tumors who meet study enrollment criteria. The main questions it aims to answer are:~what is the maximum tolerated dose and recommended dose for phase 2?~how safe and tolerable is TOS-358 at different dose levels when taken orally once or twice per day?