Tumor marker CA-125 as an evaluator and response indicator in ovarian cancer: its quantitative correlation with tumor volume

Abstract

Background: The tumor marker Cancer Antigen 125 (CA 125), though not ovarian cancer specific, is widely used for the evaluation of suspected and under-treated ovarian cancer. Many studies show that serum CA 125 level demonstrates ovarian tumor burden and its response, but they lack quantitative correlation between the two. Instead, they rely on clinical or radiological assessment of gross tumor burden. This study examines ovarian tumor volumes and corresponding serum CA 125 values before and during chemotherapy. MATERIALS/ METHODS: Ovarian tumor volume was measured by CT scans at pre-chemotherapy and after each cycle of chemotherapy in 15 patients. Blood serum CA 125 was determined on the days of CT scans using a one-step immunoenzymatic assay. Results: There was no statistically significant correlation (r = 0.18, p > 0.05) between ovarian tumor volumes and CA 125 among patients at pre-chemotherapy or any subsequent time. In individual patients, the reduction or increase in tumor volume correlated with the corresponding CA 125 values during chemotherapy in 85% (12 out of 14) of patients. Mean CA 125 halving time was 44.1 days, which correlated with tumor halving time (r = 0.63, p < 0.05). Conclusions: Values of CA 125 cannot be used for comparison of ovarian tumor mass among patients. However, serial estimation of CA 125 in individuals is fairly reliable in terms of the course of the tumor. CT scan is a more informative response indicator, but it is costly and hence may be supplemented by the easy and economical CA 125 estimation.