Papillary Renal Neoplasm With Reverse Polarity Is a Distinct Distal Nephron-Derived Tumor With Unique Methylation Profile

Papillary renal neoplasm with reverse polarity (PRNRP) has been proposed as a distinct subtype of renal cell neoplasm with recurrent KRAS mutations and indolent behavior. However, its epigenetic landscape is poorly understood. In this study, 12 PRNRPs and a PRNRP initially diagnosed as "papillary adenoma" were analyzed. All 13 cases underwent targeted next-generation sequencing for driver mutations. Eleven PRNRPs were profiled using the Illumina MethylationEPIC array and compared with a reference cohort of 71 common renal cell tumors. KRAS mutations were identified in 12 of 13 (92%) cases of PRNRP. Copy-number analysis from methylation profiling showed that 9 of 11 (82%) PRNRPs lacked copy-number changes. Two cases showed a focal loss of chromosome 8 and a gain of chromosome 16, respectively. Unsupervised clustering based on methylation data showed that PRNRPs form a distinct epigenetic group, separate from papillary renal cell carcinomas (pRCCs) and other major renal tumors, but with the closest affinity to clear cell papillary renal cell tumors. In addition, DNA methylation analysis suggested PRNRP may arise from the distal nephron, in contrast to pRCC, which appears to recapitulate proximal tubules. These findings support PRNRP as a subtype of renal cell neoplasm with a distinct epigenetic signature.