CLASSIFICATION OF TUBULO-PAPILLARY RENAL CORTICAL TUMORS USING ESTIMATES OF NUCLEAR VOLUME

The classification of renal cortical tumours is problematic, with no c lear division of benign from malignant tumours. Unbiased stereological estimates of volume-weighted nuclear volume (nuclear nu(v)BAR) were o btained by point sampling of nuclear intercepts in a retrospective stu dy of 36 variably sized tubulo-papillary basophilic cell renal cortica l tumours. There was no clear pattern of evolution of nuclear nu(v)BAR with increasing macroscopic tumour diameter. Estimates of nuclear nu( v)BAR, could not distinguish between 21 tumours classified as renal ad enomas with macroscopic diameters < 3 cm (average nuclear nu(v)BAR = 2 41 mum3) and 15 tumours classified as renal cell carcinomas with diame ters > 3 cm, or aggressive histological pattern (average nuclear nu(v) BAR = 229 mum3) (2p = 0.68). In this subtype of renal cortical tumours , estimates of nuclear nu(v)BAR do not support the historical conventi on of using a 3 cm tumour diameter as the dividing line between adenom as and carcinomas, but support the theory of a single group of tumours . As most of the truly incidental renal cortical tumours are less than 1 cm in diameter, this limit could be considered. Such small benign c ortical nodules have never been reported to metastasize, and would thu s be excluded from being diagnosed and registered as malignant. Althou gh this dividing line is again arbitrary, and cannot be justified by t he stereological measurements, it is a practical solution to a clinica l problem. There were too few examples of disease progression to asses s the prognostic significance of nuclear nu(v)BAR in these tumours.