Papillary renal neoplasm with reverse polarity (PRNRP) is a newly defined entity with distinct histomorphology and recurrent KRAS mutation. It has been estimated to constitute 4% of previously diagnosed papillary renal cell carcinoma (PRCC). Renal papillary adenoma (PA) is suggested to be the precursor of PRCC. The study aimed to investigate the association between PRNRP and PA, particularly the morphologically similar type D PA.
Nephrectomy specimens of PRCC and PA from our 10-year pathology archives were retrieved and reviewed. GATA3 immunohistochemistry and RAS/BRAF testing were performed in all cases reclassified as PRNRP and all PAs with sufficient materials. Overall, PRNRP accounted for 9.1% (10/110) of PRCC and there was no recurrence/metastasis with a mean follow-up period of 39 months. Three novel morphologic features were described, including clear cell change, mast cell infiltration, and metaplastic ossification. Nine of the 10 PRNRPs showed diffuse and strong GATA3 expression and KRAS missense mutations at codon 12. One case exhibited moderate GATA3 staining on 80% of the tumor cells and RAS/BRAF wild-type. In a total of 73 PAs, 11 were classified as type D. GATA3 expression was significantly more frequent in type D versus non-type D PAs (100% vs 35%, P<0.01). KRAS missense mutations were identified in 6/8 (75%) of the type D PAs but none of the 18 non-type D PAs.
Type D PA was different from other types of PA and represented an analogue or a small-sized PRNRP for their identical morphology, immunophenotype, and molecular signature.

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