Immunofluorescence detection of casein in human mammary dysplastic and neoplastic tissues

To detect and localize casein in human mammary dysplastic and neoplastic tissues, an indirect immunofluorescence method has been devised. Anti-casein antibodies have been obtained from rabbits immunized with casein isolated from human milk. Cryostat sections post-fixed in alcohol and paraffin sections from routinely formalin-fixed tissues proved suitable. The immuno-fluorescence method revealed the presence of casein in epithelial cells in mammary dysplasia and in some, but not all, cases of carcinoma of the breast. Well differentiated (Grade I) carcinomas were shown to contain casein, mainly localized at the inner border of the epithelial cells; the milk protein was present also in cells metastatic in lymph nodes. In Paget's disease of the nipple, casein could be detected in neoplastic cells in the ducts and also in cells identifiable with the typical intra-epidermal Paget cells. This finding is evidence of a functional differentiation of Paget cells along lines proper to the mammary epithelium.