Heterogeneity in breast cancer and the problem of relevance of findings

Many attempts are made to identify critical genetic events responsible for the development and progression of breast cancer. There is increasing evide nce that breast cancer is a heterogeneous disease, both, phenotypically as well as with respect to its molecular biologically. It is, therefore, extre mely difficult to establish a diagnostically and prognostically relevant tu mourigenesis model. Emerging new techniques such as microarrays, will provi de us with a wealth of additional data over the next years. The precise sam pling of tumour material in clearly defined histopathological lesions will be a prerequisite for the assignment of specific genetic alterations to def ined stages of breast disease.