Compared to matched comparators, tumours diagnosed during the second trimester were significantly more often ER negative, while tumours diagnosed during the third trimester were significantly larger, more often had distant metastases, were ER and PR negative, and of luminal HER2-positive, HER2-positive or TNBC subtypes (Figure 1; Supplementary Figure S1 and Table S4, available at https://doi.org/10.1016/j.esmoop.2024.102972). Here, ESR1 is linked to neoplasm.