One of the most frequent gene alterations
One of the most frequent gene alterations in MM is methylation of the p15 and p16 genes in the 5′ upstream region. P15 and p16 proteins are moxalactam regulators involved in the inhibition of transition from G1 to S phase. Frequencies of p15 or p16 gene methylation up to 32% and 53%, respectively, have been reported in MM cases.14, 15, 16, 17, 26, 37 Previous investigations have demonstrated that p16 methylation is more frequent in MM than in MGUS,13, 17, 42 whereas others reported identical frequencies.16, 26 Guillerm et al described frequencies of methylation of the p15 and p16 genes not significantly different among MGUS and MM samples and also between stage I/II and stage III, suggesting a lack of association with malignant transformation from MGUS to MM and a possible contribution to plasma cells immortalization. In line with these authors, we showed that p15 and p16 gene methylation is present at similar rates in MGUS and MM cases, supporting the concept that an alteration of the regulation of cell cycle, namely, in the transition of G1 to S phase, is a very early event in the history of MM. A reduced number of reports compared the methylation status of tumor suppressor genes among MGUS, SMM, and MM. As in the current study, Seidl et al considered SMM as an individual subgroup, but the number of patients included was also low (n = 5), resulting in nonsignificant differences when compared with MGUS. The p53 tumor suppressor gene is the most frequently mutated gene in human cancer (∼50% of human tumors), resulting in a decreased apoptosis in response to DNA damage.4, 43 However, this is rare in MM, but increases with disease progression8, 9, 44, 45 being relatively infrequent in MM at diagnosis, occurring in 0% to 3% of patients, and reaching up to 20% of patients with advanced disease.8, 46 P53 gene methylation was reported in 32% to 55% of the samples from myeloma cell lines. This finding is in contrast with our results concerning p53 methylation, which was observed in a low number of MM and MGUS cases (2% and 5%, respectively). These discrepancies may be related to the sample type (cell lines vs. patients\' samples). Another objective of the current study was to examine possible correlations between clinical and laboratorial features of MGUS, SMM, and MM and the methylation pattern of the 4 evaluated genes at diagnosis. We found that patients with p16 gene methylation were more likely to have advanced ISS stage and an increased serum creatinine level. We also observed a significant association between p15 methylation and elevated lactate dehydrogenase, as well as between DAPK gene methylation and an immunoglobulin-A subtype. These findings may suggest that hypermethylation of the studied genes is associated with a more aggressive disease phenotype. Looking at cytogenetic abnormalities, we did not find any association between the methylation pattern of any of the 4 evaluated genes and the presence of chromosome 13 deletion, t(4;14), t(11;14), or 17p deletion by fluorescence in situ hybridization. These results are in accordance with those of Braggio et al and Walker et al in all mentioned cytogenetic subgroups, except for t(4;14), which was associated with a poor prognosis. The loss of CD27 in MGUS has been linked to MM progression, and the loss of CD56 expression was associated with extramedullary spreading, aggressive disease, and inferior progression-free survival, but not overall survival. CD117 expression in clonal plasma cells is associated with favorable biological features and a lower frequency of adverse cytogenetic characteristics. MM plasma cell expression of CD28 in newly diagnosed patients is a major prognostic predictor of poor clinical outcome, allowing MM cells to better survive to treatment and resulting in their selective outgrowth. In a multivariate analysis, we evaluated possible correlations involving methylation profile of p15, p16, p53, and DAPK and each specific immunophenotypic marker (CD27, CD28, CD56, and CD117), and no statistically significant associations were found. To the best of our knowledge, this is the first study to investigate possible associations between immunophenotypic features and methylation status of tumor suppressor genes in plasma cell dyscrasia.