Mucinous tubular and spindle cell carcinoma of kidney: A distinct morphologic entity of renal cell carcinoma

Mucinous tubular and spindle cell carcinoma (MTSCC) is a rare morphologic variant of renal cell carcinoma (RCC) characterized by an epithelial-tubular proliferation admixed with spindle cell areas and a myxoid or mucinous stroma. It was initially referred as an unusual renal carcinoma with prominent spindle cell change, RCC with loop of Henle differentiation, low-grade myxoid tumor, and low grade collecting duct carcinoma.^1-6 In 2004, it has been recognized as a distinct entity of RCC in the 2004 World Health Organization tumor classification.^7,8 Since then, several dozen of MTSCCs have been reported with additional complementary morphologic features, immunohistochemical profiles, and cytogenetic changes that have further clarified its clinicopathologic features.^9-14 It was initially thought to be a "low-grade" renal cell tumor because of its bland nuclear features and indolent behavior. However, it has became clear that MTSCC has a histological spectrum ranging from low to high grade that includes, rarely, sarcomatoid differentiation. In addition to nodal metastasis, distant metastasis and death of patients have been described.^15-17 Herein, we present a case of MTSCC and summarize the current knowledge regarding histological and immunohistochemical features, differential diagnosis, and prognostic factors.