Immunohistochemical study for O6-methylguanine-DNA methyltransferase in the non-neoplastic and neoplastic components of gliomas

Abstract

Although the expression O6-methylguanine-DNA methyltransferase (MGMT) is an important hallmark for decision of nitrosourea chemotherapy for glioma patients, no immunohistochemical method for analysis of MGMT has been standardized yet. Gliomas usually contain non-neoplastic cells even deep in the tumor. It is not known which of these components expresses MGMT. To clarify this point, we investigated MGMT expression in the non-neoplastic cells in autopsy and surgical specimens by immunohistochemistry. High grade gliomas were also studied to find a cut-off point for treatment decision. MGMT immunohistochemistry in the normal brain or brain with non-neoplastic disease revealed nuclear staining in some endothelial cells, inflammatory cells, ependymal cells, astrocytes and oligodendroglias. Some cells were double stained with CD68 (macrophages or microglias). The neurons were consistently MGMT-negative. High grade gliomas always contained an MGMT-positive non-neoplastic component. Although, the endothelial cells were easily distinguished from the neoplastic cells, other cells were often mistaken for tumor cells. The population of MGMT-positive non-neoplastic cells was usually less than 10%. We set a cut off-point at 10% between the positive and negative groups because the statistical difference in the overall survival was most distinct at this value. In 51 high grade glioma patients, who received both radiotherapy and chemotherapy with nimustine (ACNU), the median overall survival of the MGMT-negative group (23 months) was significantly longer than that of the MGMT-positive group (14 months) (P < 0.009). Multivariate analysis revealed that the negative MGMT expression was a significant prognostic variable next to the degree of surgical removal for the overall survival. In the MGMT-positive group, addition of platinum-based chemotherapy did not improve the survival.

Correlation of histomorphologic prognostic markers and proliferative index with loss of heterozygosity 1p/19q and MGMT status in diffusely infiltrating gliomas

“…MIB-LI ( 5%/>5%) and tumour grade (grades II/IV). The cut-off value so determined was 10.50%, which was similar to Nakasu et al 27 However it is suggested that a larger population size with proper follow-up data be studied, in order to ensure a better correlation of this value.…”

Promoter methylation and expression analysis of MGMT in advanced pediatric brain tumors

“…Nakasu et al analyzing neoplastic and non-neoplastic cells of gliomas, found that tumors always presented an MGMT-positive normal cell component. Considering a cut-off point at 10% of the normal cell component in glioma samples for discriminating the negative tumor from the positive one, they showed that MGMT negative expression tumor was a significant factor for survival (P<0.05) in the patient treated with ACNU (20).…”

MS-MLPA: an attractive alternative laboratory assay for robust, reliable, and semiquantitative detection of MGMT promoter hypermethylation in gliomas

“…With regard to the first question, it is important to note that MGMT expression was reported to be present in non-neoplastic endothelial cells, astrocytes, oligodendroglial cells, and in inflammatory cells within a glioma. 23 Furthermore, it has been demonstrated that MGMT expression can be induced by glucocorticoids, ionizing radiation, and genotoxic agents, including those used during chemotherapy. [24][25][26] Determination of the hypermethylation status of the MGMT promoter therefore remains warranted, as it provides information on the ability of the tumor cells to express AGT independent of their expression levels before chemotherapy.…”