[A Case of Recurrent Breast Cancer with Multiple Bone Metastasis Effectively Treated by CDK4/6 Inhibitor in Addition...

We report a case of recurrent breast cancer with multiple bone metastasis in a 62-year-old woman. Her breast cancer (invasive ductal carcinoma, T2N0M0, Stage ⅡA)was resected in 2001(partial mastectomy plus axillary lymph node dissection) with adjuvant chemotherapy(UFT)and irradiation to her left remnant breast. In February 2018, she complained of severe pain in right femoral joint and hip. CT scan showed a left cystic breast tumor(17 cm)and multiple bone metastasis. The core needle biopsy of the costal bone lesion and left mastectomy were performed. These pathological findings were recurrence of the breast cancer(ER+). The endocrine therapy(exemestane, aromatase inhibitor), the administration of denosumab and irradiation to painful bone lesions were performed, but it did not suppress tumor progression. The treatment of letrozole plus palbociclib(CDK4/6 inhibitor)were continued for 3 months from May 2018, and this therapy made her bone lesions smaller, but palbociclib were stopped due to its severe neutropenia. After that, the single administration of letrozole was continued, but the tumor marker did not become normal. In February 2019, abemaciclib was administered in addition to letrozole. One year later, her symptoms improved and her bone metastases have showed partial response.