H2AX protein levels were analysed by immunohistochemistry (IHC) in three classes of human BC with distinct clinical outcomes and myofibroblast content: Luminal‐A (LumA), ERBB2‐amplified (HER2) and Triple‐Negative (TN) tumours (Fig 4; Table 1 for cohort description). Here, H2AX is linked to neoplasm.