FISH Scoring on Paraffin Sections Versus Single-cell Suspension for Chromophobe Renal Carcinoma and Renal Oncocytoma

BACKGROUND: Sectioning of the nuclei on tissue sections may give an overestimate of monosomy, a feature diagnostic of chromophobe renal cell carcinoma versus renal oncocytoma. The aim of the study was to assess whether or not nuclear sectioning may distort the results obtained from interphase fluorescence in situ hybridization (FISH) comparing the data obtained from analysis of isolated nuclei derived from formalin-fixed, paraffin-embedded sections with histological sections from the adjacent sections from the same tumors. PATIENTS AND METHODS: Five chromophobe renal cell carcinomas and five renal oncocytomas were recruited. Sections of 5 μm and 30 μm were cut for FISH to investigate chromosomes 1, 2, 6 10 and 17. RESULTS: FISH of isolated nuclei from renal oncocytomas showed a mean increase of 3.0% for nuclei with two signals when compared to tissue sections. For chromosomes 2, 6, 10 and 17, isolated nuclei showed a mean increase of 4.9% of fluorescent signals over nuclei from tissue sections. FISH analysis of isolated nuclei from chromophobe renal cell carcinoma showed a similar counts. CONCLUSION: When a tumor section exhibits a borderline percentage of nuclei with single signals around the cut-off level on tissue sections, the test should be repeated on isolated nuclei to confirm chromosomal loss, diagnostic of chromophobe renal carcinoma.