Analysis of the p53 pathway in CLL. (A) FISH with a green fluorescent chromosome 17 centromeric probe and a red 17p probe demonstrating the deletion of 17p in most, but not all, CLL cells. (B) Single-nucleotide polymorphism microarrays in CLL. The patient has loss of heterozygosity in part of the genome covered by the p53, suggesting that the CLL clone may have no active p53. The orange shaded area in the figure indicates a deletion of 17p. Direct sequencing is then possible. (C) Direct sequencing allows the identification of single p53 mutations. These mutations are often found when the other allele is deleted, although this is not the case here.