TP53 and B-cell chronic lymphocytic leukemia: However, in these studies, TP53 reactivation was achieved in cell lines expressing a missense mutational p53, while in many CLL cases with aberrant TP53 expression, deletion of the short arm of chromosome 17 (del17p13) results in a complete loss of TP53, often in association with TP53 mutations on the other allele (77).