CDKN2A and astrocytoma (excluding glioblastoma): In order to define an appropriate cutoff value for interpreting CDKN2A FISH results as positive for homozygous deletion in routine clinical service, and to assess the anticipated impact of applying these results in our patient population using the proposed cIMPACT-NOW grading schemes, we performed a retrospective analysis of IDHm astrocytomas that had prospectively undergone CDKN2A FISH analysis.