BRCA1 and neoplasm: It has been suggested that endocrine agents such as TAM will not be effective in preventing breast cancer in BRCA1 mutation carriers because the majority of tumours (up to 80%) arising in these women are oestrogen receptor α (ERα) negative, have a high mitotic rate and are of high histological grade (Lakhani, 1999; Lakhani et al, 2002).