Casein and alpha-lactalbumin detection in breast cancer cells by immunocytochemistry.

Casein and alpha-lactalbumin are characteristic proteins produced by normal mammary cells under hormonal stimulation. Specific antisera were used to immunochemically stain for these two proteins in the unstimulated R3230AC transplantable rat mammary tumor as well as in normal lactating rat mammary tissue. Specific staining was observed in the lactating rat alveolar epithelial cells and in the cells lining the intraalveolar ducts with both antisera. In the R3230AC tumor some cells were shown to contain casein or alpha-lactalbumin; the majority of the tumor cells were unstained. These findings indicate that normal mammary cells as well as a small population of cells within the R3230AC tumor are actively synthesizing casein or alpha-lactalbumin. Furthermore, the results suggest that immunocytochemistry may be used to determine the functional heterogeneity of mammary tumors directly.