Palbociclib, Letrozole & Venetoclax in ER and BCL-2 Positive Breast Cancer

At commencement of study: Venetoclax will commence at 100 mg daily (oral) for days 1-21 of each 28 day cycle. This is a dose finding study so doses will be adjusted between 100 and 800 mg/day depending on dose escalation results and recommendation of the safety committee.

At commencement of study: Palbociclib will commence at 100 mg daily (oral) for days 1-21 of each 28 day cycle. This is a dose finding study so doses will be adjusted between 75 and 125 mg/day depending on dose escalation results and recommendation of the safety committee.

Letrozole will be dosed daily at a fixed dose of 2.5 mg/day throughout the study.