Mucinous tubular and spindle cell carcinoma (MTSCC) is rare in renal cell carcinoma (RCC) and usually demonstrates a low nuclear grade and a better prognosis compared with other RCCs. The authors present a case report of MTSCC containing an area of Fuhrman nuclear grade 3, in addition to an area with a micropapillary pattern. An 82-year-old man consulted a hospital due to macrohematuria, and a tumor in the right kidney was detected. The tumor was resected and histologically examined. The tumor consisted of various growth patterns: Elongated tubular structure, a papillary structure containing a micropapillary pattern and solid pattern with spindle cells. The tumor cells demonstrated Fuhrman nuclear grades 2 and 3. Invasion into the lymph vessel and metastasis into the regional lymph node were observed. Thus, the tumor was diagnosed as a high grade MTSCC. Five months following resection, a computed tomography scan suggested metastasis of the tumor into the para-aortic lymph nodes and liver, and the patient succumbed to brain metastasis. When MTSCC of kidney is observed, careful histological observation is important to avoid missing a high nuclear grade area.
Keywords: metastasis; micropapillary pattern; mucin-poor variant; mucinous tubular and spindle cell carcinoma; renal cell carcinoma.