While the sarcoma entities with high levels of genomic instability signatures are known to carry complex karyotypes including complex rearrangements in their genomes, the pathogenesis of synovial sarcoma (SS) is associated with a unique chromosomal translocation that results in the expression of the fusion gene SS18‐SSX, and mutations in the CTNNB1 or APC genes are the most common cause of desmoid tumors (DT; Cancer Genome Atlas Research Network, 2017b; Kim et al, 2018; Knijnenburg et al, 2018), most likely explaining the observed differences in the signatures. The gene discussed is APC; the disease is desmoid tumor.