New and emerging renal entities: a perspective post-WHO 2016 classification

Renal tumours include a heterogeneous and diverse spectrum of neoplasms. Recent advances in this field have significantly improved our understanding of the morphological, immunohistochemical, molecular, epidemiological and clinical characteristics of renal tumours, which led to the new Vancouver classification of renal neoplasia and the new World Health Organization (WHO) classification of renal cell tumours. This review aims to summarise the new information and evidence on several new and emerging/provisional renal entities, which were mostly generated after the recent classification of renal neoplasia. We include in this review the following new and emerging/provisional renal entities: succinate dehydrogenase-deficient renal cell carcinoma, thyroid-like follicular carcinoma of the kidney, anaplastic lymphoma kinase rearrangement-associated renal cell carcinoma, renal cell carcinomas with prominent smooth muscle stroma, fumarate hydratase-deficient renal cell carcinoma, biphasic squamoid papillary renal cell carcinoma, eosinophilic solid and cystic renal cell carcinoma, atrophic kidney-like renal cell carcinoma, clear cell renal cell carcinoma with giant cells and emperipolesis, Warthin-like papillary renal cell carcinoma, and low-grade oncocytic renal tumour (CD117-negative; cytokeratin 7-positive). Some of these entities, such as succinate dehydrogenase-deficient renal cell carcinoma, have already been recognised as new entities in the WHO classification, and some have been recognised as provisional/emerging entities. However, we include in this review several additional entities that, on the basis of the published evidence, also warrant this designation. We hope that this review will ease the navigation through this complex and evolving field, and will inform and stimulate new studies and discussions.