A Study of Sirolimus (Albumin-Bound) in Combination With Palbociclib and Fulvestrant for the Treatment of Advanced Breast Cancer

Sirolimus (albumin - bound): Dose escalation, intravenous infusion

Palbociclib: the dosage is 125 mg, orally once a day. taken continuously for three weeks followed by a one - week break, with a treatment cycle of four weeks

Fulvestrant: the dosage is 500 mg, intramuscular injection. It is given on the 1st and 15th days of the first cycle, with a treatment cycle of four weeks. After that, it is administered once every four weeks.