The factors used in planning breast cancer treatment and predicting the course of disease at the present level of scientific development are presented. The most significant independent prognostic factor is the presence or absence of malignant cells in regional lymph nodes. Affected lymph nodes at the higher levels, their number and size as well as the penetration of malignant cells through the capsule all decrease the chance of survival. Factors relating to the tumor and on which the fate of the patient depends to a great extent are its size, histologic type and maturity. The penetration of malignant cells into lymph and blood vessels of the breast as well as tumor necrosis are prognostic factors of unfavorable progress of the disease. Steroid hormone receptors in the tumor simplify the choice of later systemic treatment. Poor outcome of the disease is also indicated by intensive growth of malignant cells, the presence of epidermal growth factor receptors, of the oncogen c-erb B-2 and some proteases.