Clinical uses of tumor markers: A critical review

Tumor markers are molecules that indicate the presence of malignancy. They are potentially useful in cancer screening, aiding diagnosis, assessing pro gnosis, predicting in advance a likely response to therapy, and monitoring patients with diagnosed disease. Because of the low prevalence of most canc ers in the general population and the limited sensitivity and specificity o f available markers, these tests alone are generally of little value in scr eening for cancer in healthy subjects. Currently, however, PSA in combinati on with digital rectal examination and CA 125 together with ultrasound are undergoing evaluation us screening modalities for prostate and ovarian canc er, respectively. Again, because of a lack of sensitivity and specificity, markers are rarely of use in the early diagnosis of cancer. As prognostic i ndicators, markers may provide information that is independent of tradition ally used factors or within subgroups defined by traditional criteria, for example, urokinase plasminogen activator in node-negative breast cancer. At present, the best available marker for predicting response to therapy is t he estrogen receptor for selecting hormone-sensitive breast cancers. Many d ifferent markers can be used in the surveillance of patients with diagnosed malignancies, the most useful of these being HCG in trophoblastic disease and both AFP and HCG for nonseminomatous testicular germ cell tumors. In ge neral, thr:currently available tu mor markers lack sensitivity for early ca ncer and specificity fur malignancy. The goal of future research should he to develop more sensitive and specific markers, especially for the common c ancers.