Evaluation of MSA as a serum marker in breast cancer: a comparison with CEA.

In a blind study, 518 serum samples were assayed for serum levels of mammary serum antigen (MSA) by an enzyme immunoassay (EIA) using the 3E1.2 monoclonal antibody. Using 300 IU as the arbitrary cut off to distinguish normal from abnormal individuals, 75% of patients with primary Stage I carcinoma of the breast (n = 12), 89% of those with Stage II (n = 9) and 93% of those with Stage IV (n = 57) had elevated levels of MSA. A relationship was observed between the level of MSA and stage of disease, and therefore with the extent of tumour burden. Levels of MSA were also determined in a series of 19 patients undergoing chemotherapy for breast cancer. Over a 2-24 month period, the change of MSA levels corresponded with the clinical course of the disease in 17 (89%) cases. MSA levels were also raised in some patients with ovarian, colon, lung and kidney cancer, but the average level was lower than in patients with breast cancer. A comparison of CEA and MSA levels in these patients revealed that MSA was a substantially better marker for breast cancer than CEA. The results of this study demonstrate that MSA levels are elevated in patients with breast cancer and may provide a useful means of following the clinical course of patients with this disease.