Two cases of osteoblastic bone metastasis from muscle-invasive bladder cancer with discrepancy in response to chemotherapy: problems and limitations of bone biopsy.

We report two cases of muscle-invasive bladder cancer (MIBC) with increasing multiple osteoblastic bone lesions but shrinking other lesions in response to chemotherapy. Case 1 had MIBC and received radical cystectomy followed by adjuvant gemcitabine plus cisplatin chemotherapy (GC). Three years after, follow computed tomography (CT) showed development of multiple lymph node metastasis, and then we performed GC as a first-line systemic chemotherapy. After two cycles of GC, CT showed de novo multiple osteoblastic lesions although metastatic lymph nodes were shrunk. Biopsy of the sternum revealed metastatic urothelial carcinoma. Case 2 had MIBC with multiple osteoblastic lesions on CT and bone scintigraphy, which was initially diagnosed as cT3bN0M1. After one cycle of GC, the number of osteoblastic lesions obviously increased although bladder tumor was regressed. Since the clinical course was unusual, biopsy of the clavicle was done. The histological diagnosis was benign osteoblastic bone disease, then the clinical diagnosis was revised to non-metastatic MIBC, and radical cystectomy was performed. Ten months after surgery, the patients complained worsening backache and CT showed increase in number of osteoblastic lesions. Eventually, ilium biopsy revealed bone metastasis of urothelial carcinoma. In case of atypical finding and unusual clinical course, biopsy of suspected metastatic lesion may be informative although adequate sampling should be secured. © The Japan Society of Clinical Oncology 2020.