Expression of OCT3/4 in renal medullary carcinoma represents a potential diagnostic pitfall.

Renal medullary carcinoma (RMC) is a rare aggressive renal tumor that classically afflicts young black patients with sickle cell trait. The tumor shows overlapping pathologic and clinical characteristics with collecting duct carcinoma and urothelial carcinoma, which often results in a diagnostic conundrum. When the tumor presents in a metastatic site in the absence of a history of renal tumor, germ-cell tumor is often a primary diagnostic consideration, given the young age of most patients. OCT3/4 is an immunohistochemical marker that is routinely used in clinical practice and is widely considered to be a specific marker for germ-cell tumor. We studied the pathologic and immunohistochemical characteristics of 14 cases of RMC. Immunohistochemical staining for OCT3/4 staining was noted in 10/14 RMCs with strong nuclear staining in 8 cases and was absent in all cases of collecting duct carcinoma and urothelial carcinoma. OCT3/4 expression is not specific to germ-cell tumor and is seen in the majority of RMC cases. Caution must be exercised in interpreting the presence of OCT3/4 staining in a poorly differentiated neoplasm, especially at a metastatic site as a germ-cell tumor, as this may represent a potential diagnostic pitfall.