The Decalcification of Cervicothoracic Spinal Metastasis of Breast Cancer Due to Discontinuation of Denosumab: A Case Report

Breast cancers frequently metastasize to bone. Several guidelines recommend denosumab to control metastasis. In the current case, denosumab allowed the calcification of cervicothoracic spinal metastases following bone decalcification by breast cancer. Six years after administration, denosumab was discontinued and the metastatic lesions became decalcified, but recalcification occurred after re-administration of denosumab. There were no reports of serious decalcification after discontinuation of denosumab. The patient was a 71-year-old woman who was unable to walk independently because of a fracture of the seventh cervical vertebra and severe spinal cord compression. After immobilization with a halo vest, posterior fixation was performed. Examination of the pathology of the breast and cervical spine revealed ductal carcinoma of the breast. After docetaxel for four months, tegafur-gimeracil-oteracil potassium (TS-1) was administered and monthly denosumab was initiated. CT showed postoperative recalcification of the cervicothoracic spine, and MRI revealed spinal cord decompression. The first occurrence of medication-related osteonecrosis of the jaw (MRONJ) occurred five years after cervicothoracic spinal surgery and the second occurrence of MRONJ occurred after six years. Denosumab was discontinued and TS-1 was resumed four months after discontinuation. Fourteen months after discontinuation of denosumab, the patient felt muscle weakness in the right upper extremity and numbness in both hands. CT showed cervicothoracic spine decalcification and MRI showed spinal cord compression. As there were no signs of recurrence in the primary lesion around the left breast, TS-1 was continued and denosumab was resumed. Three months after the re-administration of denosumab, CT showed recalcification and recovery of upper extremity muscle strength, and MRI revealed improvement in spinal cord compression.