PIK3CA and histiocytic sarcoma: Genomic findings in a large cohort of histiocytic sarcoma using a targeted next‐generation sequencing (NGS) approach identified driver alterations that involved the RAS‐MAPK signalling pathway (MAP 2K1, KRAS, NRAS, BRAF, PTPN11, NF1 and CBL) (57%), the PI3K signalling pathway (PTEN, MTOR, PIK3R1 and PIK3CA) (21%) and the tumour‐suppressor gene CDKN2A (46%).16