ATRX and astrocytoma (excluding glioblastoma): Interestingly, the analysis of TERT promoter mutations and ATRX mutations in glioblastomas, astrocytomas, oligodendrogliomas, and oligoastrocytomas showed that these two mutations were mutually exclusive, thus indicating that these tumors use two different molecular mechanisms to activate telomerase activity: either TERT promoter mutations were increasing telomerase expression or ATRX mutations were inducing mechanisms of alternative telomere lengthening, not requiring telomerase activity [18].