Deletions, predominantly monoallelic, of chromosome 17p13 region containing the TP53 gene locus occur in about 10% of untreated MM cases [15–17]; the incidence rate reported in PCL ranges from 35% to 75% [12, 18], and is particularly high (more than 50%) in HMCLs [19]. The gene discussed is TP53; the disease is plasma cell leukemia.