Study on Abemaciclib with Tamoxifen or Alone for Women with Metastatic Breast Cancer

Inclusion Criteria

• Have HR+ and HER2- breast cancer.
• Cancer has returned or worsened after hormone therapy.
• Have had at least two chemotherapy treatments, with one or two given for metastatic cancer.
• Have measurable cancer as per standard criteria.
• Have a performance status of 0 or 1, meaning fully active or restricted in physically strenuous activity but ambulatory.
• Have stopped previous cancer treatments for a certain period before starting the study drug and have recovered from any side effects.
• Have good organ function.
• Have a negative pregnancy test and agree to use effective birth control during the study and for three weeks after the last dose.
• Can swallow pills.

Exclusion Criteria

• Have signs or history of cancer spread to the brain or spinal cord.
• Have a history of certain heart conditions like unexplained fainting or irregular heartbeats.
• Have an active bacterial or fungal infection needing IV antibiotics or a detectable viral infection.
• Have previously used a CDK4/6 inhibitor.
• Have a chronic condition causing ongoing diarrhea.
• Have had another type of cancer in the past three years, except for certain skin or cervical cancers.