PIK3R1 and dyskeratosis congenita: All three DC cases (no. 20–22) carried MLH1 and POLD1 mutations with TMB-H and MSI-H, and exhibited variable mutations in PTEN, ARID1A, PIK3CA, PIK3R1, and CTNNB1. The TERT coding region was mutated in two DC cases, although the promoter was not.