The survival of patients with breast cancer depends on parameters known as prognostic factors. The first generation of prognostic factors are simple, have been validated, and have proved their usefulness. We know the importance of examining axillary lymph nodes. However, because there has been a constant increase in the percentage of patients with no invaded lymph nodes, tumor size has become an important parameter. The 10-year survival rate of patients with tumors less than 1 cm in diameter exceeds 90% suggesting that there might seem to be no need for adjuvant therapy. According to histological grade assessed by the Scarff-Bloom and Richardson method, grade I tumors have a better prognosis than grade II or III tumors. Knowledge of the concentration of estrogen and progesterone receptors in tumors provides not only prognostic information but also indicates whether hormone therapy is justified. All these first generation factors are intimately linked and, taken together, they are the main factors on which the oncologist bases his decision whether or not to prescribe adjuvant therapy. There is still no consensus regarding the assay methods and normal levels of second generation prognostic factors. Amongst these factors, the most promising are those, like S-phase determination by flow cytometry, that evaluate cell proliferation potential and those that investigate tumor invasiveness by assaying urokinase plasminogen activator or its inhibitor.