Mucinous tubular and spindle cell carcinoma of the kidney with neuroendocrine differentiation: Report of two cases

We encountered 2 cases of mucinous tubular and spindle cell carcinoma (MTSCC) during a short time. In a 61-year-old man who had macroscopic hematuria for 1 month, the 14.5 × 14.0 × 12.0-cm resected tumor involved the right middle aspect of the renal parenchyma and compressed the renal pelvis. In an asymptomatic 47-year-old man, a renal tumor was found during an annual physical examination. The 3.5 × 3.0 × 2.0-cm tumor was located at the upper pole of the right kidney. The histologic findings in both cases were similar. Tumors consisted of tightly packed, small, elongated tubules separated by pale mucinous stroma. The tumor cells were cuboidal to spindled with eosinophilic cytoplasm and low nuclear grade. Mitoses were few or nonexistent and without abnormal figures. Both tumors were immunoreactive for cytokeratin (CK) cocktail (AE1/AE3), high-molecular-weight CK (34βE12), low-molecular-weight CK (35βH11), CK7, epithelial membrane antigen, E-cadherin, and vimentin. The tumor cells also were reactive for neuron-specific enolase, chromogranin, and synaptophysin. The ultrastructure of the tumor cells contained abundant mitochondria, junctional complex, and dense-core neurosecretory granules. We present 2 additional cases of MTSCC showing typical morphologic features with neuroendocrine differentiation.