Study has two parts, Part 1 (dose escalation) and Part 2 (dose expansion). Part 1 is divided into Parts 1A, 1B, 1C and 1D and Part 2 is divided into Parts 2A, 2B and 2D. In Part 1A, single escalating doses of PF-07248144 alone will be administered to determine the maximum tolerable dose (MTD) and select the recommended dose for expansion (RDE). In Part 1B,1C and 1D, PF-07248144 will be administered in combination with either fulvestrant (Part 1B); palbociclib + letrozole (Part 1C) or PF-07220060+fulvestrant (Part 1D).. After the determination of the monotherapy RDE in Part 1A, PF-07248144 will be evaluated in a dose expansion cohort as a monotherapy in Part 2A.~After determination of the combination RDE from Part 1B, PF-07248144 in combination with fulvestrant, PF-07248144 will be evaluated in a combination dose expansion with fulvestrant in Part 2B. In Part 1C, PF-07248144 in combination with letrozole + palbociclib will be evaluated for dose finding to determine the MTD and RDE for this combination. After determination of the triple combination RDE from Part 1D, PF-07248144 in combination with PF-07220060 + fulvestrant will be evaluated in a combination dose-expansion cohort, Part 2D.
This is an open-label, multi center study to evaluate safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of PF-07248144 and early signs of clinical efficacy of PF-07248144 as a single agent and in combination with either fulvestrant or letrozole + palbociclib or with PF-07220060 + fulvestrant