Clinical applications of serum and tissue markers in malignant disease: breast cancer as the paradigm

Within the past few years, the measurement of serum and tissue markers, especially the latter, has assumed a more significant role influencing clinical decisions about treatment and follow-up of patients with malignant disease. Breast cancer is a useful paradigm to illustrate the types and importance of these various markers. Tissue markers, including nuclear grade, steroid hormone receptors, DNA index, ploidy, expression of oncogenes or tumor-suppressor genes, epidermal growth factors, cathepsin D, proliferating cell nuclear antigen (PCNA), Ki-67, p32, and others, may influence choices of initial treatment as well as adjuvant chemotherapy and (or) hormone administration. The serial measurement of serum markers, those currently available and those on the horizon, for example, may offer a way to monitor patients at risk for recurrent cancer. Although the current role of these markers may be controversial, as information about them is collected and refined, in the future perhaps a panel of such studies could be incorporated into forthcoming clinical staging systems for carcinoma of the breast and other malignancies to define both treatment and outcome.