Th pathobiology of breast cancer is complex: clinically "early" breast cancer may be tumor biologically "late" progressing rapidly toward death. Accordingly, it has been suggested that two different breast cancer populations (slow tumor growth and long survival-fast tumor growth and short survival) exist, which cannot be identified by pathohistological criteria. However, these "populations" are most likely either patients with localized disease and occult metastases (long survival) or with diagnosable regional and occult or overt systemic spread (short survival). Since even small tumors (0.1 to 0.3 cm in diameter) can spread systemically, in most patients breast cancer upon clinical diagnosis may be considered an inevitably lethal disease. Present treatment modalities can only improve the quality of life and delay death, even though the overall long-term survival rates of breast cancer are better or at least equal to those of other cancers. However, with other cancers (Table 2) it is decided within the first 5 years which patients are cured because the survival rates for 5, 10, 15, and 20 years are similar. In contrast, survival rates of patients with breast cancer steadily decline and there is no point in time when patients can feel really safe; this is indicative of a peculiar tumor pathobiology of this disease, the nature of which remains to be investigated. Progress in the fight against breast cancer is only possible by application of sensitive physical, reliable immunological, and specific biochemical methods for early diagnosis and development of efficient therapeutic modalities for inhibition of growth or complete eradication of metastasized cancer cells.
