A Case of Advanced Late Recurrence of Hormone Receptor Positive Breast Cancer Successfully Treated with Abemaciclib and Anastrozole

BACKGROUND In step with the aging of the Japanese population, late recurrence of hormone receptor positive (HR+) breast cancer occurring especially beyond 20 years after the initial diagnosis has been recognized as not rare anymore, as it has been occurring at a constant rate lately. The administration of an aromatase inhibitor with a CDK4/6 inhibitor has become the gold standard in Japan for cases of recurring HR+ breast cancer without severe visceral metastasis. CASE A 73- year-old woman was diagnosed by chance with late recurrence of HR+ breast cancer 21 years after undergoing radical resection followed by adjuvant anastrozole for 5 years for stage Ⅲb right breast cancer. Asymptomatic multiple bone metastases on her ribs and sternum with bilateral lung metastasis and malignant effusion all disappeared while she was on a year- long administration of anastrozole and an optimal dose of abemaciclib(100 mg bid). However, because of the Grade 3 digestive adverse event that occurred at approximately 1 year of treatment, she could only maintain the treatment for up to 13 months. After then, no recurrence has been detectable for 6 months so far. CONCLUSION CDK4/6 inhibitors, in combination with anastrozole, will play a pivotal role in the initial approach to elderly patients with HR+ late recurrence as a chemotherapy- free strategy.