[A Case of Postoperative Pulmonary Metastasis of Breast Cancer with Complete Response by Abemaciclib plus Fulvestrant Therapy].

A 66-year-old woman underwent total mastectomy with level Ⅰ and Ⅱ axillary lymph node dissection for right breast cancer in July 2007. The pathology results indicated the presence of T2N0M0 invasive ductal carcinoma(tubule forming type), that was estrogen receptor-positive and human epidermal growth factor 2-negative. She received postoperative adjuvant therapy with oral anastrozole(ANA)for 5 years. Eleven years after surgery, at the age of 77 years, a chest X-ray examination during a routine health checkup identified a mass shadow in the right lung. Further investigation revealed bilateral multiple lung metastases due to breast cancer recurrence. Histological examination of a tissue obtained by computed tomography(CT)-guided lung biopsy confirmed that the histological type and subtype were identical to those found in the initial surgery. Hence, endocrine therapy with ANA plus CDK4/6 inhibitor was started in November 2018. However, the first CDK4/6 inhibitor, palbociclib, caused severe myelosuppression even when the dose was reduced by 2 levels. Therefore in January 2019, the patient was switched to abemaciclib, with the dose reduced by 1 level initially and then reduced by 2 levels from August 2019. In June 2019, new multiple lung metastases appeared, and the patient was switched from ANA to fulvestrant, after which complete response was achieved in 6 months. CT in June 2021 showed no recurrence, and the patient(now 80-year-old)continues to take abemaciclib plus fulvestrant therapy.