Immunohistochemical studies of DMBA-induced rat mammary tumors.

In order to clarify the biological characteristics of rat mammary tumors induced by 7,12-dimethylbenz-[a]-anthracene (DMBA), histochemical and immunohistochemical studies were performed. Two types of luminal spaces were observed within the tumor. In one type, the lumen was surrounded by eosinophilic columnar cells which were strongly reactive for soybean agglutinin (SBA) but weakly stained with keratin antibodies. In the luminal spaces, substances positive for PAS, dialyzed iron ferrocyanide or alcian blue and resistant to mucopolysaccharidase were occasionally observed. Ultrastructurally, the luminal surface was characterized by the presence of microvilli and tight junctions. In the other type, the lumen was often found in highly cellular foci and surrounded by pale, polygonal or elongated cells which were weakly stained with keratin antibodies but not SBA. The luminal spaces presented a peculiar structure filled mainly with mucoid substances sensitive to hyaluronidase, chondroitinase ABC and heparitinase, and the inner surface of the spaces was surrounded by basement membrane components: laminin, fibronectin and type IV collagen. The results of the present study therefore showed that DMBA-induced mammary tumor consists, partly, of a structure resembling human adenoid cystic carcinoma.