Study on Endocrine Therapy With or Without Abemaciclib After Surgery for Breast Cancer

Inclusion Criteria

• Men and women aged 18 or older.
• Diagnosed with early-stage breast cancer that is hormone receptor positive (HR+) and HER2 negative (HER2-), with no signs of cancer spreading to distant parts of the body.
• Must have had surgery to remove the primary breast tumor.
• Must have tumor tissue available for additional testing.
• Must have cancer that has spread to lymph nodes and meets at least one of the following high-risk criteria:
  • Cancer in 4 or more lymph nodes
  • Tumor size of 5 cm or larger
  • High tumor grade (grade 3)
  • High Ki-67 index (20% or more)
• Must join the study within 16 months after breast cancer surgery.
• Can have up to 12 weeks of hormone therapy before joining the study.
• Must have recovered from any side effects of previous treatments like chemotherapy, radiation, or surgery.
• Women who can become pregnant must have a negative pregnancy test and agree to use effective birth control.
• Must be in good overall health with a performance status score of 0 or 1.
• Must have normal organ function.
• Must be able to swallow pills.

Exclusion Criteria

• Cancer that has spread to distant parts of the body or no cancer in lymph nodes.
• Inflammatory breast cancer.
• History of breast cancer, except for certain cases treated over 5 years ago.
• Pregnant or breastfeeding women.
• Previous treatment with CDK4 and CDK6 inhibitors.
• Currently taking hormone therapy like birth control or hormone replacement.
• Previous hormone therapy for breast cancer prevention.
• Serious medical conditions that could affect participation.
• History of certain heart conditions or blood clots.
• Active infections or high viral load.
• Participation in another clinical trial within the last 30 days.