Low nuclear and cytoplasmic CYP2S1 was significantly associated with high‐grade tumours (p ≤ 0.009), intermediate Nottingham prognostic index (NPI) group (p ≤ 0.025), high mitotic frequency (p ≤ 0.002), human epidermal growth factor receptor 2 (HER2)‐negative disease (p ≤ 0.011), and ductal carcinoma (p ≤ 0.022). This evidence concerns the gene ERBB2 and breast ductal adenocarcinoma.