World Health Organization Classification of Tumours Pathology and ...

Multilocular cystic renal cellcarcinomaJ.N. EbleDefinitionA tumour composed entirely of numerouscysts, the septa of which contain smallgroups of clear cells indistinguishablefrom grade Ι clear cell carcinoma.ICD-O code 8310/3Clinical featuresThere is a male:female predominance of3:1. All have been adults (age range 20-76 years, mean = 51) {650}. No instanceof progression of multilocular cystic renalcell carcinoma is known.MacroscopyWhile cysts are common in clear cellrenal cell carcinomas, only rarely is thetumour entirely composed of cysts. Inthese tumours the number of carcinomacells is small and diagnosis is challenging{1835}. In order to distinguish thesetumours with excellent outcomes fromother clear cell carcinomas, ones containingexpansive nodules of carcinomamust be excluded and diagnosed simplyas clear cell renal cell carcinoma {650}.Multilocular cystic renal cell carcinomaconsists of a well-circumscribed mass ofsmall and large cysts filled with serous orhaemorrhagic fluid and separated fromthe kidney by a fibrous capsule.Diameters have ranged from 25 mm to130 mm. More than 20% have calcificationin the septa and osseous metaplasiaoccasionally occurs.Tumour spread and stagingNo tumour with these features has everrecurred or metastasized.HistopathologyThe cysts are usually lined by a singlelayer of epithelial cells or lack an epitheliallining. The lining cells may be flat orplump and their cytoplasm ranges fromclear to pale. Occasionally, the liningconsists of several layers of cells or a fewsmall papillae are present {2561}. Thenuclei almost always are small, spherical,and have dense chromatin.The septa consist of fibrous tissue, oftendensely collagenous. Within some of thesepta there is a population of epithelialcells with clear cytoplasm. The epithelialcells resemble those lining the cysts andalmost always have small dark nuclei.The clear cells form small collections butFig. 1.23 Multilocular cystic renal cell carcinoma.do not form expansile nodules. Theseepithelial cells often closely resemblehistiocytes, or lymphocytes surroundedby retraction artefacts. Increased vascularitywithin the cell clusters is a clue totheir nature.ImmunoprofileThe cells with clear cytoplasm in thesepta frequently react strongly with antibodiesto cytokeratins and epithelialmembrane antigen and fail to react withantibodies to markers for histiocytes.ABFig. 1.24 Multilocular cystic renal cell carcinoma. A The septa of multilocular cystic renal cell carcinoma contain eptihelial cells which can be mistaken for lymphocytes.B The epithelial cells in the septa of multilocular cystic renal cell carcinoma react with antibodies to epithelial markers. EMA expression.26 Tumours of the kidney