Viability of CLL cells after in vitro administration of fludarabine. Metabolic WST-1 assay was used. Dark gray bars indicate biallelic TP53 defect (n = 7); Light gray bars, monoallelic TP53 defect (n = 7); white bars, no TP53 defect (n = 8); the last group consisted of 4 samples harboring ATM deletion and 4 purely wt samples with unmutated IgVH. The monoallelic TP53 defects (missense mutations) impaired the response to fludarabine in comparison with the other high-risk CLL factors, ie, deletion of ATM or unmutated IgVH locus.