Carcinoembryonic antigen. A useful monitor of therapy of small cell lung cancer.

In 85 patients with small cell cancer of the lung, the degree of carcinoembryonic antigen (CEA) elevation correlated with the extent of disease. Normal CEA levels (less than 2.5 ng/mL) occurred in 55% of patients with limited disease compared with 12% of patients with extensive disease. All patients with CEA levels greater than 50 ng/mL had liver involvement. Serial CEA levels were useful in monitoring response to chemotherapy and in predicting relapse. All patients with CEA values greater than 5.0 ng/mL before start of treatment had a fall in CEA level with response to treatment and a rise in CEA level when resistance to chemotherapy developed. In patients with CEA levels of less than 5.0 ng/mL at the start of treatment, rising values reflected the onset of recurrent disease in 10 or 21 patients who had relapses. The CEA levels used in conjunction with standard roentgenograms and organ scanning studies can aid in the initial staging of small cell cancer of the lung, and in monitoring treatment.