Histological preservation after in situ hybridization to archival solid tumour sections allows discrimination of cells bearing numerical chromosome changes.

In this study, non-isotopic in situ hybridization (ISH) was used for the cytogenetic and histological examination of urological (prostatic adenocarcinoma) and endocrine (phaeochromocytoma) tumour cell nuclei in 4 microns paraffin-embedded tissue sections. In order to investigate preservation of tissue morphology, standard heat denaturation was compared with a mild enzymatic treatment for the production of single-stranded (ss)-DNA for ISH. Numerical analysis by ISH with chromosome-specific repetitive DNA probes for chromosomes 1, 7, and 11 revealed overrepresentation of chromosome 7 in the phaeochromocytoma (P < 0.01). The constitutional underrepresentation of the Y chromosome was easily detected in the prostate tumour (P << 0.01) when probed for chromosomes 7, 16, and Y. The enzymatic treatment appeared superior to heat denaturation with respect to tissue architecture in the phaeochromocytoma, while no clear difference was observed in the prostatic cancer. ISH probe patterns were similar for the two types of denaturation in both tumours (P > or = 0.20). We conclude that (1) ISH can be used for the identification of numerical cytogenetic changes in solid tumour cell nuclei within archival tissue sections; and (2) mild 'denaturation' protocols, replacing heat, are preference in retaining tissue architecture in fragile tumour specimens.