TP53 and B-cell chronic lymphocytic leukemia: Therefore, although deletion or mutation of TP53 gene in previously untreated CLL patients are reported to be 10-15% [7,8,18], the frequency of TP53 dysfunction increases to nearly 50% of patients when the disease progresses following initial therapies [19,20], suggesting that DNA damaging therapies exert a selective pressure that may lead to TP53 inactivation and subsequent resistance to commonly used chemotherapeutic agents.