[METASTATIC Mucinous Tubular and Spindle Cell Carcinoma Treated with Nivolumab Successfully : A Case Report].

A 68-year-old man was referred to our hospital with a right-sided renal tumor identified by ultrasonography at the time of his medical check-up. Computed tomography revealed a well-circumscribed but distorted mass measuring 64×45×57 mm in the right kidney with para-aortic lymph node swelling. Laparoscopic right nephrectomy with para-aortic lymphadenectomy was performed. Histopathological diagnosis was mucinous tubular and spindle cell carcinoma (MTSCC) (pT3a) without lymph node metastasis (pN0). Postoperatively, metastases were identified in the lungs, and the vertebral and iliac bones. The patient was treated with axitinib. The lung nodule progressed and left sacrum metastases appeared even after treatment with axitinib. Therefore, nivolumab was administered as second-line treatment. The metastases in the lungs, as well as vertebral and iliac bone showed complete response to this therapy. MTSCC of the kidney is a rare low-grade renal cell carcinoma without any established systemic therapy for metastatic or unresectable lesions. We report a case of metastatic MTSCC in a patient who showed a favorable response to nivolumab treatment. This is the first report to describe successful treatment of metastatic MTSCC with anti-programmed cell death 1 antibody.