The number of tumor-related features available to predict the prognosis of patients with breast cancer has grown impressively in recent years. Histology, tumor stage, and lymph-node status are now supplemented with measurements of steroid hormone receptors, ploidy, S-phase fractions, growth factors, oncogenes, and oncogene products. Cellular and molecular biology have not only advanced the understanding of carcinogenesis, but have provided a host of new biologic measures potentially related to clinical outcome.

Interest in prognostic factors has been stimulated by the success of systemic adjuvant therapy for early-stage, operable cancer of the breast. Any feature of a tumor, or combination of features, that accurately indicates which patients are destined for recurrence and which are not is of considerable importance. Patients destined for recurrence can be selected for systemic adjuvant therapy, while patients who will not have a recurrence can be spared the morbidity of a treatment that offers no benefit. In addition, refinement of prognostic information facilitates improved clinical testing by ensuring comparability of treatment groups and providing markers to measure the success or failure of specific therapies.