NI-1 METHYLTHIOADENOSINE PHOSPHOLYLASE STATUS CORRELATES WITH PROGNOSIS AND METHIONINE UPTAKE IN IDH MUTANT ASTROCYTOMA

PURPOSE: Methylthioadenosine phosphorylase (MTAP) immunohistochemistry staining has been proposed as a surrogate of Cyclin-dependent kinase inhibitor 2A homozygous deletion (CDKN2A HD) in various type of tumors. This study was designed to determine whether MTAP status correlates with clinical outcome and uptake of 11C-methionine in astrocytoma with IDH mutations. METHODS: We conducted a MTAP immunohistochemistry staining of 30 IDH-mutant astrocytoma patients who underwent 11C-methionine positron emission tomography scans prior to surgical resection from 2000 to 2020. The tumor-to-normal ratio (T/N) of 11C-methionine uptake was calculated by dividing the mean standardized uptake value (SUV) for the tumor by the mean SUV of the normal brain. RESULTS: Eight of the thirty astrocytomas harboring IDH mutations exhibited loss of cytoplasmic MTAP expression, which is accompanied with a poor prognosis. The median progression free survival (PFS) in IDH-mutant astrocytoma patients with loss of MTAP was 1.88 years, significantly shorter than that of those with MTAP retention (6.80 years, p=0.003). The median Overall survival (OS) in IDH-mutant astrocytoma patients with loss of MTAP was 5.23 years, again significantly shorter than that of those with MTAP retention (p=0.0191). Multivariate analysis revealed MTAP status to be an independent prognostic marker for PFS in IDH-mutant astrocytoma patients. The median T/N ratio in tumors with loss of cytoplasmic MTAP expression was 2.12 (IQR 1.92-2.50), i.e., significantly higher than that of tumors with MTAP retention (1.65, IQR 1.23-1.94, p=0.0116, U test). CONCLUSION: Our study showed MTAP status to correlate with clinical outcome and T/N ratio of astrocytoma patients with IDH mutations.