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A Study to Evaluate the Safety and Tolerability of TOS-358 in Women With HR+ HER2- Breast Cancer
A Study to Evaluate the Safety and Tolerability of the Covalent Phosphoinositide-3-Kinase (PI3K)-Alpha Inhibitor, TOS-358, in Adult Subjects With Select Solid Tumors
Who can join
Ages 18 and older · Women
Full eligibility criteria
Key Inclusion Criteria * Locally advanced, recurrent, or metastatic HR +/HER2- breast cancer * Up to 3 prior lines of therapy for metastatic disease * Willing and able to provide written informed consent for this study * Adults ≥ 18 years old at time of consent * Known PIK3CA mutations or amplifications as determined at a CAP/CLIA-certified or equivalently accredited diagnostic laboratory using a validated test * Measurable or evaluable disease by RECIST 1.1 * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 * Life expectancy ≥ 6 months, as determined by the investigator * Adequate bone marrow, liver, and kidney function within 14 days prior to first dose of investigational product * Fasting plasma glucose \<= 140 mg/dL AND hemoglobin A1c (HbA1c) \<= 7.0% * Available archived or fresh tumor tissue sample for detection of PIK3CA mutation by central laboratory test Key Exclusion Criteria * Has an established diagnosis of diabetes mellitus type 1 or has uncontrolled diabetes mellitus type 2 * Known active central nervous system (CNS) metastases * PTEN mutations
About the study
The goal of this clinical trial is to evaluate the safety and efficacy of TOS-358 in women with HR+ HER2- metastatic breast cancer whose tumors have a mutation in PIK3CA and who meet all other study enrollment criteria. The main questions it aims to answer are:
1. Phase 1a: what is the maximum tolerated dose and recommended dose for phase 2? 2. Phase 1a: how safe and tolerable is TOS-358 at different dose levels when taken orally once or twice per day? 3. Phase 1b: how safe and effective is TOS-358 when given with standard of care medicines for HR+HER2- metastatic breast cancer (fulvestrant and CDK4/6i)
What is being tested
- TOS-358 (drug)
- Fulvestrant (drug)
- Palbociclib (drug)
- Ribociclib (drug)
Sponsor: Totus Medicines · Participants: 241 · Started: Feb 15, 2023
Contact the study team
- Clinical Trials · Phone: Please e-mail
Official record on ClinicalTrials.gov — NCT05683418
Locations in the U.S.
Conditions
From ClinicalTrials.gov, data retrieved Sep 30, 2026. Each study sets its own eligibility; the study team decides who can join.