Mucinous tubular and spindle cell carcinomas are low-grade renal epithelial neoplasms, which were first recognized as a specific entity in the World Health Organization 2004 classification. Forty-five documented cases have been reported. We present 15 additional cases that were incidentally discovered in ten women and five men, with a mean age of 53 years. The tumor is characteristically made up of large eosinophilic regular spindle cells separated by a myxoid stroma with intercellular alcian-blue-positive clear droplets. In peripheral areas, elongated tubules and papillae covered by cubic cells are found. Until this entity had been defined, pathologists used to classify these tumors as variants of solid papillary carcinomas with compressed and elongated papillae, metanephric adenomas, and sarcomatoid carcinomas. In the literature, cytogenetic data indicate various chromosomal losses and gains, but no loss of 3p or trisomy 7 and/or trisomy 17. In two cases, we demonstrate chromosomal loss involving chromosomes 1, 4, 6, 11, 8, 13, 14, 15, 18, and 22. In our 15 cases, immunohistochemistry favored a distal tubule origin (EMA(+), AE1/AE3(+), CK7(+), CK19(+), E-cadherin(+), AMACR(+), and CD10(-)). Prognosis was favorable in our cases, while in the literature, two metastatic cases were reported. Further investigations are required to determine the frequency and true prognosis of these tumors, which are easily identifiable morphologically.
