Numerous pathologic and biologic factors have been assessed for their ability to predict clinical behaviour and response to therapy in breast cancer patients. Currently, traditional morphological features such as lymph node status, tumour size, histological type and tumour grade remain the leading prognostic factors. Steroid receptors are also important, but their main role consists in predicting response to hormonal therapy. Although several new indicators have been proposed to refine the value of the above-mentioned proven parameters, interpretation of their impact is not conclusive. In particular, immunohistochemical evaluation of p53, c-erbB-2 and MIB-1 appears to be potentially useful and considerable efforts are currently being made to technically and clinically validate them.