Efficient test for cancer antigens: decreased levels of cancer antigen in serum after excision of breast tumor.

Monoclonal antibody technology has developed new serum marker tests which may offer advantages in the follow up of cancer patients. In breast cancer detection among symptomatic patients MCA and CA 15-3 monoclonals at best reach a sensitivity of about 0.45 at a specificity level of 0.90. We have tested these monoclonal tests (MCA and CA 15-3) by applying them to detect the postoperative decrease of marker levels in the serum among women with breast cancer or benign breast disease. The CA 15-3 postoperative decrease test (5% decrease) reached slightly higher diagnostic sensitivity (0.70) and efficiency (0.83) than the MCA postoperative decrease test (sensitivity 0.65, efficiency 0.80). The combined MCA and CA 15-3 decrease tests had a sensitivity of 0.85 and an efficiency of 0.90 at 5% decrease level. The postoperative decrease test is far superior to normal marker tests in breast cancer detection, especially when several sensitive markers are used. A 35% or larger decrease in serum levels of MCA or CA 15-3 after surgery was 100% specific for breast cancer, and detected 43% of all cancer cases. Although such a test cannot be used for screening, it could be valuable in special diagnostic situations.