Collecting duct carcinoma: an entity to be redefined?

Collecting duct carcinomas (CDCs) are highly aggressive tumors with poor survival at 1 year and are often metastatic at the time of diagnosis. It has been shown that patients may have better survival when treated with a chemotherapy regimen used for urothelial carcinoma. Such tumors must therefore be recognized, but their pathological diagnosis remains difficult. The two main differential diagnoses are renal pelvis urothelial carcinoma with infiltration of the kidney and/or high-grade and high-stage papillary renal cell carcinoma. The aim of our study was to compare the immunophenotype of 14 CDCs with 6 renal pelvis urothelial carcinomas (RPUC) infiltrating the medulla. The following markers were evaluated: ulex europeus aglutinin (UEA), peanuts aglutinin, vimentin and aquaporin 3 (AQP-3), a membrane component of normal collecting duct and urothelial cells. We were able to define a reproductive urothelial phenotype AQP-3+, vimentin− and UEA+. Among the 14 CDCs, 10 cases demonstrated this immunophenotype. It coincided with an urothelial-like trabecular and tubular pattern. In contrast, the 4 remaining papillary CDCs had the inverse pattern, AQP-3−, vimentin+ and UEA−. These results suggest that: (1) the trabecular and tubular variant of CDC with the urothelial AQP-3+, vimentin− phenotype can be included in the spectrum of urothelial diseases; (2) the papillary variant probably does not belong to the same entity; (3) AQP-3 is a marker of interest for improving the histological classification of CDC and unclassified aggressive renal tumors.