| Objective:Diffuse large B cell lymphoma (DLBCL) is the most common non-Hodgkin lymphoma, showing extensive large B cells infiltrating. Due to diversity of genetic and gene expression changes, the therapeutic response and prognosis of this tumor are significantly different in individual cases. Extra-nodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) is another type of common B cell lymphoma. According to variable number of large tumor cells and their distribution, MALT lymphoma can be divided into three different types, which are MALT lymphoma with large tumor cells, MALT lymphoma without large tumor cells and DLBCL with MALT lymphoma component. However, it is usually difficult to distinguish them due to lack of definitive diagnostic criteria in morphology. In addition, the difference of prognosis between MALT lymphoma with or without large tumor cells is still unclear. In this study, the aberrant genetic alterations and gene expression changes in DLBCL and MALT lymphoma were invesigated respectively. The aims were:1) to find effective molecular prognostic signatures of DLBCL in an attempt to provide evidences for its target therapy; 2) to find molecular markers of MALT lymphoma to assist diagnosis and evaluate the prognosis in order to guide the clinical therapy.Methods:The first part:MYD88 L265P mutation, CDKN2A, CDKN2B and p53 deletion, BCL2 and MDM2 amplification were examined in 81 cases of DLBCL by multiplex ligation-dependent probe amplification (MLPA). In 293 cases of DLBCL, C-MYC translocation was detected by fluorescence in situ hybridization (FISH) and its expression was observed by immunohistochemistry (IHC). The correlation between C-MYC translocation and expression was subsequently analyzed, and 116 of them with complete follow-up data were carried on survival analysis. The relationship between aberrant genetic alterations and clinicopathological parameters was statistically analyzed, as well as the association between each factor and prognosis. The second part:To detect the C-MYC translocation and expression, FISH and IHC were performed on 20 cases of MALT lymphoma with large tumor cells,42 cases of MALT lymphoma without large tumor cells and 7 cases of DLBCL with MALT lymphoma component. Their roles in transformation of MALT lymphoma and prognostic values were also evaluated in these cases.Results:The first part:1. In the experiment of MLPA, mutation of MYD88 L265P was observed in 19.8% of DLBCL cases. Deletions of CDKN2A, CDKN2B and p53 were detected in 21.0%,14.8% and 16.0% of the cases, respectively. Both BCL2 and MDM2 amplifications were found in 16.0% of the cases. BCL2 amplification was more often found in the Ann Arbor stage Ⅰ-Ⅱ (P=0.027). p53 deletion was more frequently detected in elders (P=0.001), and MDM2 amplification was much more examined in GCB subtype (P=0.007). In univariate analysis, MYD88 L265P mutation predicted the lower overall survival (OS) and progress-free survival (PFS) (P=0.035 and P=0.004), whereas BCL2 amplification was associated with higher OS and PFS (P=0.011 and P=0.026). In the group with rituximab, patients with MYD88 L265P mutation had poorer OS and PFS (P=0.032 and P=0.003). In non-GCB subtype, MYD88 L265P mutation was associated with lower PFS (P=0.018) and BCL2 amplification was significantly correlated with better OS and PFS (both were P=0.007). In multivariate analysis, it was demonstrated that MYD88 L265P mutation was an independent risk factor for PFS in DLBCL (OS: HR=2.498,95%CI:1.128-5.533, P=0.024; PFS:HR=2.578,95%CI:1.303-5.102, P=0.007).2. In 293 cases of DLBCL, C-MYC translocation was detected in 10.2% of cases and C-MYC overexpression was in 22.9%. The frequency of C-MYC translocation was much higher in GCB subtype than that in non-GCB subtype. It was shown that C-MYC overexpression was associated with lower OS (P=0.010), and the same results were also found in GCB subtype (P=0.005). In the group of rituximab and non-GCB subtype, patients with C-MYC translocation had lower OS (P=0.046 and P=0.022). In multivariate analysis, it was manifested that the patients with C-MYC overexpression had inferior prognosis. Thus, C-MYC overexpression was an independent prognostic factor for DLBCL (HR=1.995,95%CI:1.032-3.854, P=0.040).3. We integrated all the parameters for 81 cases of DLBCL, and Cox regression analysis was then carried out in these data. It was showed that IPI, serum LDH level, therapeutic regimen and involvement of central nervous system were independent factors for OS and PFS in DLBCL, and mutation of MYD88 L265P was an independent factor for PFS in DLBCL (HR=2.578,95%CI:1.303-5.102, P=0.007). The second part:MALT lymphoma with large tumor cells was more frequently examned in extra-gastric or extra-gastrointestinal sites. C-MYC was positively expressed in 75% cases-of the group with large tumor cells, significantly higher than that in the group without large tumor cells (35.7%, P=0.004). In addition, the positive rate of C-MYC expression was higher in extra-gastric sites compared to that in gastric sites (P=0.001). None of the 62 cases of MALT lymphoma had C-MYC translocation, while C-MYC translocation was only found in one case of DLBCL with MALT lymphoma component. C-MYC expression, IPI, Ann Arbor stage and serum LDH level were considerably associated with OS according to the univariate analysis. However, only C-MYC expression≥20% showed a statistical significance in the multivariated analysis.Conclusions:A varity of aberrant genetic alterations are examined in DLBCL. MYD88 L265P mutation is an independent risk factor for PFS in DLBCL and it might be a potential therapy target in the future. C-MYC overexpression is an independent prognostic factor in MALT lymphoma and may play an important role in aggressive transformation of this disease. |
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