Deletion monitoring in skin tumors by interphase-FISH using band-specific DNA probes

Thin sections from archival paraffin blocks of various skin tumors (26 mela nomas, 15 squamous cell carcinomas, 5 keratoacanthomas, 5 basal cell carcin omas) were subjected to interphase-FISH (I-FISH) with DNA probes which are specific for chromosomal regions often involved in deletions in human cance r. These were probes for chromosome 3p21, the p53 gene on chromosome 17p13, and, in a few selected cases, a probe for chromosome 9p21. It was demonstr ated that deletions of these regions could be reliably detected and related to tumor type and histology, i.e, grading. The most common deletion was th at of 3p21 which was found in all studied squamous cell carcinomas (SCC) of low differentiation, in 60% of the Bowen carcinomas, in 70% of the metasta tic melanomas less than 1.5 mm thick, and in over 55% of those which thickn ess over 2 mm. In contrast, FISH-detected p53 deletion was a rare finding i n the investigated tumors. However, this gene was even found in an increase d copy number in 60% of the poorly differentiated SCCs (grade 4) and in 50% of the non-metastatic melanomas less than 1.5 mm thick. Deletion of 9p21 w as detected in 13 of the 14 tumors on which pertinent examinations could be performed. I-FISH was shown to be a reliable technique for the rapid detec tion of chromosome band specific deletions in archival material of human sk in tumors.