Although representing a minority of all glioblastomas, secondary glioblastomas are recognized and represent the eventual development of grade IV features in a previously grade II tumor. This is certainly suggested by the fact that this tumor is IDH1 mutated. The histology from the first biopsy may, however, have under-graded the tumor, due to not obtaining the enhancing component. This is not to say that this is not a secondary GBM, merely that it may already have been a GBM on the first study, but the highest component may have been missed.