An immunocytochemical study of alpha-lactalbumin in human breast tissue.

The distribution of the milk protein, lactalbumin, has been studied in human breast tissue by the indirect immunoperoxidase technique on formalin fixed paraffin embedded sections. It was found in all lactating breasts examined and in all breasts from subjects who were more than 18 weeks pregnant. It was also seen in a small proportion of non-pregnant, non-lactating patients usually confined to small focal secretory lobular lesions known as lactational foci but also occasionally in morphologically normal lobules. Previous pregnancy does not appear to be a pre-requisite for lactalbumin secretion and our study suggests a possible relationship with usage of hormonal preparations. A wide variety of benign and malignant breast lesions were studied and none was found to contain the protein, except for fibroadenomas from patients who were pregnant or who harboured lactional foci. The absence of lactalbumin from all 44 breast carcinomas studied suggests that it has no role to play as a marker in the histopathological diagnosis or clinical monitoring of this disease.