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 evidence that breast cancer is a heterogeneous disease, both, phenotypically as well as with respect to its molecular biologically. It is, therefore, extremely difficult to establish a diagnostically and prognostically relevant tumourigenesis model. Emerging new techniques such as microarrays, will provide us with a wealth of additional data over the next years. The precise sampling of tumour material in clearly defined histopathological lesions will be a prerequisite for the assignment of specific genetic alterations to defined stages of breast disease.