Molecular Genetic Analysis in B-cell Lymphomas : A Focus on the p53 Pathway and p16INK4a

The presence of TP53 mutations has been associated with inferior outcome in diffuse large B-cell lymphoma (DLBCL) and chronic lymphocytic leukemia (CLL). In DLBCL, the impact of the TP53 codon 72 polymorphism and MDM2 SNP309 has not been clearly elucidated, whereas MDM2 SNP309 was suggested as a poor-prognostic marker in CLL. In addition, p16INK4a promoter hypermethylation has been implicated as a negative prognostic factor in DLBCL. The aim of this thesis was to further evaluate these molecular markers in well-characterised materials of DLBCL and CLL. In paper I, we investigated the prognostic role of TP53 mutation, codon 72 polymorphism and MDM2 SNP309 in DLBCL (n=102). The presence of TP53 mutations (12.7%) correlated with a poor lymphoma-specific and progression-free survival, and a particularly pronounced effect was observed in the germinal center subtype. Neither the MDM2 SNP309 nor the TP53 codon 72 polymorphism had an impact on age of onset or survival. In paper II, we applied pyrosequencing to measure the level of p16INK4a methylation in DLBCL (n=113). Thirty-seven percent of cases displayed p16INK4a methylation; however, no clear association could be observed between degree of methylation and clinical characteristics or lymphoma-specific survival. In papers III–IV, we investigated the prognostic role of MDM2 SNP309 (n=418) and TP53 mutation (n=268) in CLL. No correlation was observed between any particular MDM2 SNP309 genotype and time to treatment and overall survival. Furthermore, no association was found between the different MDM2 SNP309 genotypes and established CLL prognostic markers. TP53 mutations were detected in 3.7% of CLL patients; where the majority showed a concomitant 17p-deletion and only three carried TP53 mutations without 17p-deletion. We confirmed a significantly shorter overall survival and time to treatment in patients with both TP53 mutation and 17p-deletion. Altogether, our studies could confirm the negative prognostic impact of TP53 mutations in DLBCL, whereas MDM2 SNP309 and TP53 codon 72 polymorphisms appear to lack clinical relevance. We also question the role of p16INKa methylation as a poor-prognostic factor in DLBCL. Finally, the presence of TP53 mutation in CLL appears to be rare at disease onset and instead arise during disease progression