Renal mucinous tubular and spindle cell carcinoma: report of four cases and literature review.

Mucinous tubular and spindle cell carcinoma of the kidney (MTSCC-K) is an unusual renal tumor. It is important to increase the recognition of the clinicopathological features of MTSCC-K and improve its clinical and differential diagnosis. This report described four cases of MTSCC-K with clinical, imaging, and pathological examination and showed that the tumor boundaries of MTSCC-K were clear, and tumor cells arranged into tubules and cord-like beams, between which was lightly stained myxoid stroma. The tumor cells were smaller and cube- or oval-shaped, with single small eosinophilic nucleoli, low-grade nuclei, and little nuclear fission. The myxoid stroma was scattered around lymphocytes and plasma cells. Immunohistochemical markers including CK7, CD117, EMA (epithelial membrane antigen), vimentin, and CK8/18, showed positive expression in tumor cells, but the tumor cells were negative for CD10 and villin. The proliferation index of Ki-67 was 5-10%. Since MTSCC-K is a rare low-grade malignancy, with unique histological and immunohistochemical characteristics, it is important for clinicians and pathologists to have a defined awareness of this tumor type in order to decrease the rate of misdiagnosis.