Surgical pathology of cystic renal cell carcinomas: is there an overestimation of malignancy?

Abstract

Most cystic renal epithelial tumors have excellent prognosis after resection despite the high proportion of renal cell “carcinoma” diagnosis. The 2019 Bosniak classification revision and recent downgrading of multilocular cystic renal cell carcinoma (RCC) to multilocular cystic renal neoplasm of low malignant potential (MCNLMP) may help reduce the discrepancy. Cystic clear cell (CC) RCC has been shown to behave favorably compared to non-cystic CC RCC and suggests a continuum with MCNLMP which would represent the most indolent of this spectrum. Further, the current pathological criteria distinguishing MCNLMP and extensively (>75%) cystic CC RCC should be revisited as both tumors show similar excellent prognosis. Clear cell papillary (CCP) RCC, which often has cystic change, should be renamed as “clear cell papillary neoplasm of low malignant potential”. However, cystic (and pseudocystic) features may also occur in other non-CC RCC types, including uncommon aggressive tumors with metastatic potential. This review highlights the need for reappraisal of the pathological categorization of cystic RCCs including the cystic CC RCC and CCP RCC.