This study is testing a new drug called TOS-358 in women with hormone receptor-positive (HR+), HER2-negative breast cancer that has spread (metastatic) and has a specific gene change called a PIK3CA mutation. TOS-358 is a type of drug called a PI3K-alpha inhibitor. The study will first look at the safety and best dose of TOS-358 alone, and then combine it with standard treatments like fulvestrant and CDK4/6 inhibitors (palbociclib or ribociclib). Researchers want to see how safe TOS-358 is and if it causes side effects. To join, you must be an adult woman with this type of breast cancer, have a PIK3CA mutation, and have had up to three prior treatments for metastatic disease. The study plans to enroll 241 participants, but its current status is unclear.

Study design

This is an interventional study with two parts: a dose-finding part and a dose-expansion part. It plans to enroll 241 women.

What's involved

You would take TOS-358 orally until your disease progresses, you experience unacceptable side effects, or for other reasons outlined in the study. Your safety will be monitored from the start of treatment until 30 days after your last dose.

Compensation

Not stated in the trial record.

Follow-up

Your safety and side effects will be monitored from the start of treatment until 30 days after your last dose.

AI-generated from the public study record. Only the study team can confirm whether you're eligible — confirm details with them before making decisions.