Papillary Renal Neoplasm With Reverse Polarity.

In 2019, papillary renal neoplasm with reverse polarity (PRNRP) was defined as a new neoplasm because it has a predominately tubulopapillary pattern lined by a single layer of cuboidal and eosinophilic cells with apically located round nuclei. Immunohistochemically, this neoplasm showed expression of GATA-3 and L1CAM and had recurrent KRAS mutations. To estimate the incidence of PRNRP and provide 8 additional cases with some variations in the morphology. We reviewed 1627 renal tumors from our hospital during a 21-year period (2000-2020). We reexamined 196 papillary renal cell carcinomas and selected those that met the diagnostic criteria for PRNRP. We found 8 cases consistent with PRNRP. The median age of the patients was 64.75 years; 7 patients were male, and 1 was female. Two patients had end-stage renal disease. No recurrence, metastasis, or tumor-related death occurred in a mean follow-up period of 67.62 months. Tumor size ranged from 1.6 to 3.7 cm. All cases were pT1. Seven cases (7 of 8; 87.5%) had predominantly cystic changes, and 1 had solid architecture. No foamy cells, clear cell change, or psammoma bodies were seen in any cases. All cases were positive for CK7, EMA, GATA3, and L1CAM. KRAS gene mutation was detected in 5 cases (5 of 8; 62.5%). PRNRP represents 4.08% (8 of 196 cases) of papillary renal cell carcinomas and 0.49% (8 of 1627 cases) of all renal tumors in the 21-year period in our series. In our study, all cases exhibited an indolent clinical course. This supports that PRNRP has characteristic morphologic and molecular features.