Factors affecting MSA levels in normal women and women with breast cancer.

Blood from 1497 women who were either non-pregnant, pregnant at all stages of gestation, lactating after parturition, postmenopausal, or who had benign breast lumps, primary breast cancer or advanced breast cancer were tested for their peripheral blood mammary serum antigen (MSA), using the 3E1.2 monoclonal antibody (MoAb) in an inhibition enzyme linked immunosorbent assay test system. The study aimed to establish normal ranges for comparison with MSA levels in breast cancer and benign breast disease. Compared with normal premenopausal women, which included women measured 8-10 times throughout their menstrual cycle, circulating MSA levels were significantly elevated throughout pregnancy (P less than 0.0001), in postmenopausal women (P less than 0.05), in women with primary breast cancer (P less than 0.05) and women with advanced (metastatic) breast cancer (P less than 0.0001). As a group, the 30 women with benign breast disease did not demonstrate significantly different MSA level from normal. However, 3% of the group did have levels above the 'cut off' for normal (400 IU/mL). Analysis of the normal premenopausal women according to age, parity and stage of the menstrual cycle and during lactation showed that these parameters did not affect MSA levels. It is concluded that the test is potentially valuable in the detection of metastatic but not primary breast cancer, and the effects of pregnancy and postmenopausal status on the circulating MSA levels need to be considered in the interpretation of MSA measurements.