As TP53 and PIK3CA mutations are among the most common genetic aberrations in breast cancers [23], we compared the VAFs of these two driver genes with those of HMCN1. Among the 64 samples harboring mutations in HMCN1, 22 and 23 also harbored mutations in TP53 and PIK3CA, respectively, and five harbored mutations in both genes. The gene discussed is PIK3CA; the disease is breast cancer.