MGMT in Primary Nodal Diffuse Large B-Cells Lymphomas: Immunohistochemical Expression and Methylation Status
S Uccella, C Placidi, S Marchet, R Cerutti, I Carnevali, D Furlan, G Pinotti, C Capella. University of Insubria - Ospedale di Circolo, Varese, Italy; Ospedale di Circolo, Varese, Italy
Background: Loss of MGMT function has been proposed as favourable prognostic marker in diffuse large B-cell lymphomas (DLBCLs). MGMT silencing is frequently caused by the hypermethylation of the promoter region. However, the relatioships between MGMT methylation status (MS) and protein expression are not clear and there are very few studies which compare immunohistochemical expression of MGMT and MS of its promoter.
Design: We studied 71 patients with primary nodal DLBCL, treated with cyclophosphamide-containing regimens and with available follow-up. MGMT-IR was detected using a specific monoclonal antibody. DLBCLs showing less than 5% of IR neoplastic cells were considered as MGMT-negative. The MS of MGMT promoter was analyzed in a subset of cases using a quantitative method based on Real Time methylation-specific PCR. For each sample we determined a percentage of methylated reference (PMR) using ActB as reference gene and we considered cases with PMR < 4 as methylated. The survival analysis was performed using the survanXL program, version 1.14.
Results: 20 /71 DLBCL (28%) were negative for MGMT at immunohistochemistry, and 19 of them were studied for MGMT methylation status. 7 of these cases (41%) showed high levels MGMT promoter methylation (M), 5 cases (26%) showed low levels of MGMT promoter methylation (U*) and 7 (33%) were unmethylated (U). We also analyzed the methylation status of 20 cases which showed MGMT immunoreactivity and 17 of them were U, 2 were U* and 1 was M. The survival analysis showed significantly longer event-free survival (EFS) in DLBCLs with high levels MGMT promoter methylation compared to U and U* DLBCLs. In addition, the presence of immunohistochemical immunoreactivity for MGMT was also associated with a significantly longer EFS. When overall survival was considered, only methylation status was a significant predictive factor.
Conclusions: These data suggest that both MGMT promoter methylation status and protein expression are prognostic factors in primary nodal DLBCLs treated with cyclophosphamide-containing regimens. Cases with low levels of methylation have the same behaviour of unmethylated DLBCLs in the survival analysis. Immunohistochemistry seems to be an useful tool to identify unmethylated cases, while a methylation analysis should be performed when there is no or low expression of MGMT.
Wednesday, March 11, 2009 9:30 AM
Poster Session V # 176, Wednesday Morning