Extent of 17p deletion analyzed by FISH using 5 markers spanning 17p and a chromosome 17 centromeric probe (D17Z1) in the 14 patients with confirmed 17p deletion. The deletion involved the p53 gene in all cases except one, but this patient (patient no. 13) had also monosomy 17, and therefore loss of one p53 allele. The proximal breakpoint was in 17q in 3 patients, as shown by deletion of D17Z1 probe, and located in 17q11 by conventional cytogenetic analysis. (FISH results in patients no. 8 and 9, where 17p deletion was not confirmed, are excluded from this figure).