Validating Serum Markers for Monitoring of Cancer

Most of the serum tumor markers available today were introduced decades ago and were applied to clinical use without rigorous evaluation of their clinical validity. Tumor markers are mainly used for monitoring the response to therapy and to facilitate earlier detection of a relapse. Many organizations have issued guidelines on the use of tumor markers, but most of the recommendations are not based on randomized prospective trials. In this issue of Clinical Chemistry , the European Group on Tumor Markers presents guidelines (MONITOR) for designing studies on the validity of tumor markers for the serial monitoring of cancer patients, with the aim of showing whether monitoring improves outcomes, compared with other routinely used methods (1). Guidelines are needed because the use of serum markers is variable and not necessarily based on evidence.The need for validating the use of tumor markers was demonstrated in the recent evaluation of cancer antigen 125 (CA125)2 measurements for monitoring patients with ovarian cancer (2). The validity of this generally accepted practice was investigated in a study that fulfilled most of the criteria in the MONITOR guidelines. Enrolled in the study were 1442 patients with ovarian cancer who had achieved complete remission with normal CA125 concentrations after undergoing platinum-based chemotherapy. Patients …