Expression of O6-methylguanine DNA methyltransferase (MGMT) and immunohistochemical analysis of 12 pineal parenchymal tumors

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Pineal parenchymal tumors (PPTs) are rare neoplasms which occupy less than 1% of primary central nervous system tumors. Because of their rare incidence, the previous reports on PPTs are limited in number and the useful molecular markers for deciding the histological grading and even selecting chemotherapy are undetermined. In this study, we conducted immunohistochemical analysis of 12 PPT specimens, especially for expression of O6-methylguanine DNA methyltransferase (MGMT) to assess whether temozolomide (TMZ) could serve as a possible alternative therapy for PPTs. We analyzed 12 PPTs consisting of 3 pineocytomas, 6 pineal parenchymal tumors of intermediate differentiation (PPTIDs), and 3 pineoblastomas. Immunohistochemical analysis was performed using antibody against MGMT, synaptophysin, neurofilament protein (NF), p53, and NeuN. Immunohistochemically, 11 out of 12 cases were positive for MGMT. The mean MIB-1 labeling index was less than 1% in pineocytoma, 3.5% in PPTID, and 10.5% in pineoblastoma. All 12 cases were positive for synaptophysin and 11 cases except 1 PPTID case showed positive for NF. Nuclear staining of NeuN was negative in all cases although cytoplasmic stain of NeuN was observed in 5 cases. No case was positive for p53. Eleven out of 12 cases of PPTs demonstrated MGMT expression, suggesting chemoresistancy to TMZ treatment. This is the first report showing MGMT expression in PPTs. In addition, MIB-1 labeling index correlated with WHO grade, although the immunoreactivity of synaptophysin, NF, NeuN, and p53 did not correlate with the histological grade.

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  • Neuropathology

    Neuropathology 32 (6), 647-653, 2012-12

    Blackwell Publishing

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