Breast epithelial antigen levels and breast tumor antigen content.

The relationship between the primary tumor expression of a breast epithelial antigen, called non-penetrating glycoprotein (NPGP) or breast epithelial mucin, and the same patient's serum level of this antigen at the time of relapse was studied in 23 cases. The expression of NPGP on breast tumors was measured by immunoperoxidase staining using monoclonal antibody Mc5, and quantitated by a histopathological index created for this purpose. Serum levels were measured by a competitive RIA using the same monoclonal antibody. An inverse correlation between these parameters was found, such that tumors having high NPGP levels in serum had a low index, while low NPGP serum levels had a high index. These results show that cellular events in breast tumors could participate in determining NPGP serum levels in breast cancer.