Evaluation of an inhibition enzyme immunoassay kit for mammary serum antigen (MSA)

The measurement of Mammary Serum Antigen (MSA) levels by a research inhibition enzyme immunoassay (EIA) using the monoclonal antibody (Mab) 3E1.2 has previously been shown to be a highly-sensitive marker in breast cancer, particularly in stage I/II of the disease process. We describe in this report, the performance of a commercial inhibition EIA kit for quantitating serum MSA and the levels of MSA found in various groups of women. The test had low intra-assay (%CV = 9.3, 40.6 units/mL, n = 40) and inter-assay (%CV = 9.0, 52.0 units/mL, n = 20) coefficients of variation and was not affected by sample addition drift in unit/mL values. Testing groups of normal women revealed that MSA levels increase with age and may be elevated in smokers and pregnant women. Using 30 units/mL as an arbitrary cut-off, 7.1% (7/98) of sera from normal women (23 smokers and 19 over 40 years) were above 30 units/mL compared to 11.8% (7/59) from patients with benign breast disease (BBD) 33.9% (18/53) from patients with pre-operative stage I/II breast carcinoma and 81.8% (35/44) with disease present at stage III/IV. These results suggest that the MSA test will be useful in monitoring breast cancer and further studies are in progress to evaluate its potential clinical utility.