COMPARATIVE FISH ANALYSIS OF NUMERICAL CHROMOSOME-7 ABNORMALITIES IN 5-MU-M AND 15-MU-M PARAFFIN-EMBEDDED TISSUE-SECTIONS FROM PROSTATIC-CARCINOMA

Interphase fluorescence in situ hybridization (FISH) was performed on 15-mu m-thick paraffin sections from prostatic carcinomas using a chro mosome 7-specific alpha-satellite DNA probe. A confocal laser scanning microscope (CLSM) was used for optical sectioning of the thick sectio ns and reconstruction of 3D images. The number of FISH signals was det ermined by a gallery of optical sections evaluating only complete nucl ei. To investiate the influence of section thickness and truncation an d nuclei on scoring results, we compared the FISH data from 15-mu m se ctions with signal counts obtained from 5-mu m sections. The latter we re evaluated by conventional fluorescence microscopy in the same tumor regions previously defined and marked on the slides. After statistica l analysis of spot frequencies in tumor and non-tumorous cells (chi(2) test), we transferred the signal frequencies into a cytogenetic class ification (-7, +7, polysomy 7). Based an this classification, most cas es showed more than one chromosome 7 aberration type. Trisomy 7 (+7) b ecame apparent in 15-mu m-thick sections in all 19 tumors, polysomy 7 (>3 spots) in 18/19 cases, and monosomy 7 (-7) in 13/19 cases. In 5-mu m sections, however, trisomy 7 and polysomy 7 were found in only 7/19 and 13/19 cases, respectively, and monosomy 7 in 7/19 cases. When com paring the classification results of tumor cells of the same tumor reg ions originating either from 5-mu m or 15-mu m sections, the following discrepancies were noted: in 15-mu m sections exclusively, in 12/19 t umors, trisomy 7 was found; in 6/19 cases, polysomy 7; in 8/19 cases, monosomy 7. The high proportion of cases with tumor nuclei expressing only one hybridization signal of chromosome 7 in 15-mu m sections coul d be confirmed as monosomy 7 in five selected cases by double-hybridiz ation using centromere-specific probes for chromosomes 7 and 12. These results demonstrate that numerical chromosome 7 aberrations are more frequently observed in thick (15-mu m) paraffin-embedded tissue sectio ns by evaluating only complete nuclei. The use of routine sections (5- mu m) for interphase cytogenetic analyses is compromised by a remarkab le underestimation of the real chromosome copy numbers.