IDH1 and neoplasm: Of the 21 tumour sets (from 31 informative cases) in which p16/CDKN2A copy number variation was identified in either the primary and/or relapse event, 11 harboured an IDH1 mutation and 10 were WT for IDH1 and IDH2, indicating that change in p16/CDKN2A copy number is equally common in IDH1 mutant and WT central conventional cartilaginous tumours.