The present invention relates to use of a PI3Kα-
mutant selective inhibitor, specifically, use of compound 1, a racemate, a stereoisomer, or a pharmaceutically acceptable salt thereof, in the preparation of a
drug for preventing and / or treating HR-positive / HER2-negative
breast cancer, colon
cancer, and
head and neck cancer. The compound 1 can inhibit the growth of HR-positive / HER2-negative
breast cancer cells, colon
cancer cells, and
head and neck squamous
cell carcinoma cells, and can be used in combination with a CDK4 / 6 inhibitor or a selective ER degrading agent, having better therapeutic
efficacy and good safety.