Among small tumours (≤ 20 mm) with no nodal spread, ER+PR−HER2− subtype of grade III was associated with a particularly high mortality (HR = 8.5, 4.0–18.2) and of similar magnitude to TNBC grade III tumours (HR = 9.2, 5.1–16.5). Here, ESR1 is linked to neoplasm.