Clinical Use of Tumor Markers Based on Outcome Analysis

Abstract

Tumor markers are substances found in the serum or urine that can be used in cancer for case-finding or screening, confirming diagnosis, estimating prognosis, monitoring response to therapy, or detecting recurrences. No tumor marker is 100% sensitive and 100% specific, but optimal clinical use can be ensured by applying appropriate cutoff points. Positive and negative predictive values are calculated to assess the efficiency of each tumor marker in a particular clinical situation. The goal is to affect patient outcome, which is the key criterion in the assessment of any laboratory test. Most tumor markers are not sensitive enough or specific enough to be used as a screening test, except for prostatespecific antigen (PSA), which is used to screen for prostate cancer. Specificity can be improved by calculating the PSA density, the PSA velocity, or the ratio of free-to-total PSA. No tumor marker with sufficient sensitivity or specificity exists to be used as a screening test for breast cancer. CA 15-3, however, is used to monitor patients after mastectomy.