PIK3CA and ductal breast carcinoma in situ: The genes most frequently mutated were PIK3CA (24% DCIS, 27% INV) and TP53 (24% DCIS, 27% INV) (Fig. 6a) and the most common amplicons were on 17q12 (ERBB2: 29% DCIS, 27% INV), 17q21.1 (GSDMB, PSMD3: 29% DCIS, 25% INV) and 11q13 (CCND1: 20% DCIS, 20% INV) (Supplementary Data Table 6).