Participants receive beltuzifan 120 mg orally once per day (QD) and palbociclib 75 mg orally QD in a 28-day schedule (21 days on followed by 7 days off), until progressive disease or discontinuation.

Participants receive beltuzifan 120 mg orally QD and palbociclib 100 mg orally QD in a 28-day schedule (21 days on followed by 7 days off), until progressive disease or discontinuation.

Participants receive beltuzifan 120 mg orally QD and palbociclib 125 mg orally QD in a 28-day schedule (21 days on followed by 7 days off), until progressive disease or discontinuation.

40 mg tablet administered orally at a dose of 120 mg.

A DLT consists of one or more of the following toxicities: Grade (Gr) 3 or 4 hypoxia or dyspnea; Gr 3 or 4 nausea, vomiting, or diarrhea if persistent for >48 hours despite therapy; Gr 3 or 4 cardiovascular, vascular, or thrombotic events; Nonhematologic AE ≥Gr 3 in severity with exceptions; Gr 3 rash that does not resolve within 2 weeks; Gr 3 nonhematologic toxicity if persisting despite optimal medical treatment; Gr 3 or 4 hematologic toxicities; Gr 3 or 4 febrile neutropenia; Gr 3 or 4 nonhematologic laboratory value; Any aspartate aminotransferase or alanine aminotransferase >8x the upper limit of normal (ULN) or 5 to 8x ULN persisting for >2 weeks; >2 weeks delay in dosing due to intervention-related toxicity; Intervention-related toxicity causing intervention discontinuation in the first 28 days of dosing; Missing >20% of intervention doses due to drug-related AEs; Gr 5 toxicity. The number of participants who experience at least one DLT will be reported.

An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. The number of participants who experience at least one AE will be reported.

An AE is any unfavorable and unintended sign, symptom, or disease temporally associated with the use of a medicinal product or protocol-specified procedure, whether or not considered related to the medicinal product or protocol-specified procedure. The number of participants who discontinued from the study treatment due to an AE will be reported.