Original ContributionWarthin-like papillary renal cell carcinoma: Clinicopathologic, morphologic, immunohistochemical and molecular genetic analysis of 11 cases

•Presenting series of distinct renal cell carcinomas with unusual morphology•All tumors were mostly papillary, composed of oncocytic cells with dense lymphocytic stroma.•Morphology resembled Warthin tumor of salivary gland, however immunohistochemical profile was typical of papillary RCC.•Chromosomal aberration pattern was variable.•Tumors followed non-aggressive clinical course in 6/9 patients, 3 patients died of disease.

Oncocytic papillary renal cell carcinoma (PRCC) is a distinct subtype of PRCC, listed as a possible new variant of PRCC in the 2016 WHO classification. It is composed of papillae aligned by large single-layered eosinophilic cells showing linearly arranged oncocytoma-like nuclei.We analyzed clinicopathologic, morphologic, immunohistochemical and molecular-genetic characteristics of 11 oncocytic PRCCs with prominent tumor lymphocytic infiltrate, morphologically resembling Warthin's tumor.The patients were predominantly males (8/11, 73%), with an average age of 59 years (range 14-76), and a mean tumor size of 7 cm (range 1-22 cm). Tumors had the features of oncocytic PRCCs with focal pseudostratification in 8/11 cases and showed dense stromal inflammatory infiltration in all cases. Papillary growth pattern was predominant, comprising more than 60% of tumor volume. Tubular and solid components were present in 5 and 3 cases, respectively. Uniform immunohistochemical positivity was found for AMACR, PAX-8, MIA, vimentin, and OSCAR. Tumors were mostly negative for carboanhydrase 9, CD117, CK20, and TTF-1. Immunohistochemical stains for DNA mismatch repair proteins MLH1 and PMS2 were retained in all cases, while MSH2 and MSH6 were negative in 1 case. Tumor infiltrating lymphocytes (TILs) consisted of both B and T cells. Chromosomal copy number variation analysis showed great variability in 5 cases, ranging from a loss of one single chromosome to complex genome rearrangements. Only one case showed gains of chromosomes 7 and 17, among other aberrations. In 4 cases no numerical imbalance was found. Follow up data was available for 9 patients (median 47.6 months, range 1-132). In 6 patients no lethal progression was noted, while 3 died of disease.In conclusion, Warthin-like PRCC is morphologically very close to oncocytic PRCC, from which it differs by the presence of dense lymphoid stroma. Chromosomal numerical aberration pattern of these tumors is variable; only one case showed gains of chromosomes 7 and 17. Warthin-like PRCC is a potentially aggressive tumor since a lethal outcome was recorded in 3/9 cases.