Comparison of mammary serum antigen (MSA) with beta 2-microglobulin (beta 2M) and carcinoembryonic antigen (CEA) assays in patients with breast cancer.

Serum levels of mammary serum antigen (MSA), beta 2-microglobulin (beta 2M) and carcinoembryonic antigen (CEA) were evaluated in 186 subjects to assess their use in the diagnosis and monitoring of breast cancer, either singly or in combination. Raised MSA levels (greater than 300 I.U.) were detected in 79% of patients with Stage I/II breast cancer, compared with 25% for beta 2M (greater than 2000 micrograms/l) and 12% for CEA (greater than 5 ng/ml) levels respectively. Of 53 patients with Stage III/IV breast cancer, 98% (MSA), 55% (beta 2M) and 64% (CEA) had raised levels. In 25 patients followed over 3-9 months, the changes in MSA levels correlated with the clinical course of the disease in 23/25 (92%), compared with 7/25 (28%) using beta 2M, and 9/25 (36%) using CEA assays. The overall sensitivity, specificity and accuracy in detecting breast cancer were 88%, 95% and 99% for MSA; 39%, 90% and 96% for beta 2M; and 38%, 95% and 98% for CEA, respectively. MSA and beta 2M assays in combination enhanced the sensitivity in the detection of breast cancer (93%) especially early breast cancer, while maintaining specificity (90%). MSA seems to be superior to beta 2M or CEA as a tumour marker in breast cancer and its levels seem to correlate with tumour burden. While it appears that beta 2M or CEA measurements used alone are of little value in the current management of breast cancer, beta 2M may be a helpful adjunct to enhance the sensitivity of MSA assay especially in early breast cancer.