Introduction Within Western Europe and the United States, breast cancer is the commonest malignancy in women. It is estimated that approximately 1:12 women will develop the tumour in their life time. Each year within the UK, there are 25 000 new cases accounting for 19% of all newly diagnosed cancers. It is the leading cause of female cancer deaths (HMSO 1991). Despite innovations in diagnosis and treatment, the effect on mortality has been modest. A major contributory factor to this limited success has been the lack of understanding about the natural history of the disease.
The problems in managing advanced disease has focused attention on detecting 'early' disease with the use of mammographic screening. This has led to the increased detection of preinvasive disease, particularly ductal carcinoma in situ (DCIS) (Molloy et al. 1989, Evans et al. 1994). This changing pattern of disease encountered by histopathologists has highlighted many deficiencies