Mucin poor mucinous tubular and spindle cell carcinoma of the kidney, with nonclassic morphologic variant of spindle cell predominance and psammomatous calcification.

Mucinous tubular and spindle cell carcinoma (MTSCC) is a rare type of kidney tumor that has only been recently described. The classic MTSCCs are polymorphic renal neoplasms characterized by small, elongated tubules lined by cuboidal cells and/or cords of spindled cells separated by pale mucinous stroma. Nonclassic morphologic variants and features of MTSC have not been well studied and rarely been reported. We report a challenging case of mucin-poor MTSCC with marked spindle cell predominance and focal psammomatous calcification in a 39-year-old man and describe its histologic and immunohistochemical features. Pathologists must be aware of the histologic spectrum of MTSCCs to ensure their accurate diagnosis.