IGF1 and breast cancer: High birthweight is an established risk factor for childhood cancers (Wilms’ tumour, infant and childhood leukaemia, osteosarcoma and astrocytoma),34 and twins have increased risks of endocrine, bone and breast cancers.35,36 The postulated mechanism is elevated levels of maternal hormone factors during pregnancy, such as estrogens and insulin-like growth factor I levels, or the aforementioned angiogenic factors.37 This mechanism could also predispose maternal cancer, and deserves further investigation.