Background/aims: The assessment of response to chemotherapy of solid tumors is generally made by measurement of tumors visualized by imaging, commonly computed tomography scanning. However, response assessment based on imaging is not always feasible because patients often have disease not measurable by imaging study, such as diffuse peritoneal dissemination. Furthermore, response assessment by imaging is expensive and time consuming. This study was carried out in an effort to evaluate the correlation between serial change on imaging and on CEA (carcinoembryonic antigen) levels for assessing chemotherapeutic response of patients with metastatic colorectal cancer.
Methodology: Between May 1998 and August 1999, a total of 40 patients with metastatic colorectal carcinoma were enrolled in this study. All the patients had to have measurable lesions. Oral tegafur-uracil 300 mg/m2/day and folinic acid 60 mg/day were administered concurrently for four weeks, repeated every five weeks, as the first-line treatment. Tumor marker CEA was examined before and during the whole course of treatment. Response based on CEA assessment was defined as a more-than 50% drop in serum CEA level for more than four weeks. The correlation between serial change on CEA and on imaging for assessing chemotherapeutic response was evaluated.
Results: Forty patients received a total of 318 courses of treatment and a response rate of 32.5% (95% confidence interval, 18.0% to 47.0%), including five complete responses and eight partial responses, was achieved by imaging studies. The pretreatment CEA levels were elevated beyond the normal cut-off value in 34 (85%) patients. The response rate evaluated by CEA assessment was 42.5% (17/40). Nine responders (22.5%) based on CEA had no remission on imaging. Agreement in assessment by imaging study and by CEA was observed in 20 patients (50%), including eight responders, five stable diseases, and seven progressive diseases. The sensitivity of falling CEA levels in the prediction of true responders on imaging was 62%. The sensitivity of elevated CEA levels for the prediction of progressive disease was 70%. Concerning the diagnostic accuracy, change in CEA levels in the prediction of true responders and progressive disease on imaging were 65% and 85%, respectively. On a follow-up of 24 months, patients with remarkable falling CEA levels survived significantly longer than non-responders (P = 0.0184, log-rank test).
Conclusions: The measurement of CEA levels might be useful in monitoring chemotherapeutic response and in predicting the prognosis of patients with metastatic colorectal cancer. Serum CEA level may be used as a means of monitoring chemotherapeutic response when imaging study is unsuitable for assessing the response in clinical practice.