RB1 and osteosarcoma: By contrast, C2 tumours were enriched for somatic point mutations in ATRX and DAXX (P = 6 × 10−5), but not RB1. The enrichment of RB1 mutations in C1 remained significant when only leiomyosarcomas and osteosarcomas were considered, confirming that this enrichment is not merely a consequence of the different distribution of tumour types across clusters.