(A) Gross pathology.
The vast majority of renal cell carcinomas occur in one kidney, and bilateral renal cell carcinomas (heterochronic or simultaneous) only account for 2%-4% of sporadic renal cell carcinomas. Renal tumors are often solitary, of which 10% to 20% are multifocal. Multifocal cases are commonly seen in patients with hereditary renal cell carcinoma as well as papillary renal cell carcinoma. The tumors vary greatly in size and are often separated from the surrounding renal tissue by a pseudo-envelope.
(ii) Classification.
Four versions of WHO classification criteria for renal tumors were introduced in 1981, 1997, 2004 and 2016. The current clinical use is the 2016 WHO 4th edition renal tumor classification criteria (Table 2), which follows the framework of the 2004 edition, with only some adjustments to the nomenclature of some more recognized tumors: for example, multifocal cystic renal cell carcinoma, which has never been reported as recurrent metastasis, is updated to low-grade malignant potential multifocal cystic renal cell tumor, and for example, Xp11.2 translocation/TFE3 fusion gene-associated renal cell carcinoma was classified as MiT family translocated renal cell carcinoma, which also includes TFEB gene-translocated renal cell carcinoma, etc. In addition, some new pathological subtypes have been added. As mentioned earlier, renal cell carcinoma can be divided into hereditary renal cell carcinoma and sporadic renal cell carcinoma based on the relationship with genetic syndromes. Hereditary renal cell carcinoma and sporadic renal cell carcinoma cannot be distinguished by pathological morphology alone.
Table 2 2016 WHO Pathologic Histologic Classification of Renal Cell Tumors