Renal cell carcinoma, unclassified with medullary phenotype: poorly differentiated adenocarcinomas overlapping with renal medullary carcinoma.

Renal medullary carcinoma (RMC) is a highly aggressive renal cell carcinoma arising in the collecting system and requiring careful correlation with status of sickle cell trait. A panel of international experts has recently proposed provisional diagnostic terminology, renal cell carcinoma, unclassified, with medullary phenotype, based on encountering an extraordinarily rare tumor with RMC morphology and immunophenotype in an individual proven not to have a hemoglobinopathy. Herein, we extend this observation to a cohort of 5 such tumors, morphologically similar to RMC, lacking SMARCB1 expression by immunohistochemistry, but each without evidence of a hemoglobinopathy. The tumors arose in 4 men and 1 woman with a mean age of 44 years, occurring in 3 left and 2 right kidneys. Clinically, aggression was apparent with involvement of perinephric adipose tissue in all 5 cases, nodal metastasis in 4 of 5 cases, and death of disease in 4 of 5 cases within 3-27 months. Histologic sections showed poorly differentiated adenocarcinoma, often with solid and nested growth patterns, as well as infiltrative glandular, tubulopapillary, cribriform, or reticular growth. Rhabdoid and sarcomatoid cytomorphology was seen in a subset. All tumors showed PAX8 nuclear positivity and SMARCB1 loss, with OCT3/4 expression in 4 of 5 cases. In summary, this first series of renal cell carcinoma, unclassified, with medullary phenotype documents tumors with morphologic, immunophenotypic, and prognostic features of RMC occurring in individuals without sickle cell trait. Although greater biologic and molecular understanding is needed, the available evidence points to these cases representing a sporadic counterpart to sickle cell trait-associated RMC.