The neighbouring CCO‐deficient duct (Figure 3B, Ci) was not related to this; however, it was clonal for a heteroplasmic 957 G > A mutation (Figure 3Cii, areas 3 and 4), and this was also not present in the surrounding CCO‐normal DCIS (Figure 3Ciii, area 5). This evidence concerns the gene RYR1 and ductal breast carcinoma in situ.