Immunoelectron microscopic localization of DF 3 cancer-associated antigen in human breast cancer

Breast cancer cells are characterized by frequent occurrence of the DF 3 breast-cancer associated antigen in the cytoplasmic area. This study elucidated the details of this cytoplasmic reactivity by immunoelectron microscopy. In infiltrating breast carcinomas, the DF 3 antigen was localized in rough endoplasmic reticulum (rER), perinuclear space, Golgi complex, membrane-bound granules and along the outer surface of cell membrane. The antigen was also accumulated in the cytosol. In contrast to this, benign lesions showed localization of the DF 3 antigen mainly along the outer surface of apical cell membrane and rarely in rER or cytosol. The present study indicated that the DF 3 antigen was of secretory type and commonly localized on the outer surface of apical cell membrane in both malignant and benign lesions. Carcinoma tissues were further characterized by frequent occurrence of immunoreactivity related to the process of antigen synthesis. The diffuse cytosolic reactivity may be associated with disordered transportation of the antigen in the cytoplasm.