When compared to IHC score 0 cases, there was statistically significant correlation between HER2‐low cluster and low tumour grade (P < 0.001), lower pleomorphism score (P = 0.001) and low mitotic count (P < 0.001), less DCIS within tumour (P < 0.001) and more lymph node metastasis (P = 0.03) (Supporting information, Table S3). This evidence concerns the gene ERBB2 and ductal breast carcinoma in situ.