Study on Palbociclib After CDK and Endocrine Therapy for Breast Cancer (PACE)

Inclusion Criteria

• Have hormone receptor positive (HR+) HER2 negative breast cancer that has spread or cannot be removed by surgery.
• Men and women, including pre- and postmenopausal women, are eligible.
• Must have shown progression on previous endocrine and CDK 4/6 inhibitor therapy.
• Must have been treated with a CDK 4/6 inhibitor and endocrine therapy before.
• Can have had up to one prior line of chemotherapy for metastatic cancer.
• Must be 18 years or older.
• Must have normal organ and bone marrow function based on specific blood tests.
• Women of childbearing potential and men must agree to use effective contraception during the study and for 60 days after the last dose.
• Must be able to swallow pills and understand the study requirements.

Exclusion Criteria

• Have had recent endocrine, chemotherapy, or biologic therapy within 14 days before starting the study.
• Have active brain metastases unless stable and not requiring steroids.
• Have discontinued prior Palbociclib due to side effects or needed more than one dose reduction.
• Have severe allergies to Palbociclib or similar drugs.
• Are taking medications that strongly affect liver enzymes or prolong the QT interval.
• Have had an organ transplant.
• Have uncontrolled illnesses like infections, heart disease, or diabetes.
• Have active autoimmune diseases that could worsen with treatment.
• Are pregnant or breastfeeding.
• Have had another cancer within the last 3 years, except for certain non-threatening cancers.