[Long-Term Response to CDK4/6 Inhibitor for Multiple Metastases of Breast Cancer]

The patient was a 60-year-old woman. She was diagnosed with hypertension, symptomatic epilepsy, renal failure, and cerebral infarction. During follow-up, she was found to have a mass in her left breast and was referred to our department. An irregular mass measuring 5 cm in diameter was palpated in the C region of the left breast. Multiple enlarged lymph nodes, thought to be metastases, were also palpated in the ipsilateral axillary lymph nodes. A needle biopsy revealed invasive ductal carcinoma, ER positive, PgR positive, HER2 negative, Ki-67 12%. A systemic examination revealed bone metastasis. Surgery was not possible due to comorbidities, so fulvestrant(500 mg/month)+denosumab(120 mg/month)was started. Furthermore, as the tumor markers were elevated, abemaciclib(300 mg/day)was added, which resulted in a decrease in the tumor markers. After 1 month of administration, grade 3 neutropenia was observed, so the dosage was reduced to 200 mg/day. During the course of treatment, the tumor markers rose again, so the dose was increased to 250 mg/day, which resulted in a decrease in the tumor markers and good tolerability. At present, 36 months after the start of treatment, long SD has continued, no adverse events of grade 3 or higher have been observed, and the drug has been well tolerated.