alpha-Lactalbumin in human and subhuman primate normal mammary tissue and in human breast cancer as a marker for prolactin activity.

Abstract

Abstract Mammary tissue from virgin, nulliparous, and multiparous primates of various species has been shown to contain α-lactalbumin, a milk protein. Production of α-lactalbumin by these tissues in organ culture was maintained or increased under the influence of prolactin. These findings provide evidence that mammary tissues, even in animals that are not pregnant or lactating, are active and responsive to prolactin. The fact that α-lactalbumin was found in 48.5% of homogenates of histologically normal breast tissue from women with breast cancer, many of whom were menopausal, indicates that this protein can be produced in humans under conditions of relative hormonal dormancy. Fewer specimens of human breast cancer (23.5% of homogenates and 21% of tissues in organ culture) were found to contain or produce α-lactalbumin. Studies on normal and cancer tissue from the same patients, 9 of 17 of whom had measurable quantities of α-lactalbumin in normal but none or much lower concentrations in cancer tissue suggest that during malignant transformation some epithelial cells may lose the ability to produce α-lactalbumin and by inference the sensitivity to prolactin. Even though some tumors may not contain α-lactalbumin, a significant minority of human tumors do. In addition, this milk protein was present in higher concentrations in cancer than in normal tissue in two individuals, and prolactin more than doubled α-lactalbumin production in three cancers maintained in organ culture. Although the presence of α-lactalbumin in tumors may suggest a responsiveness to prolactin, the possibility that the actual growth of α-lactalbumin-containing or -producing tumors is dependent on prolactin must await clinical confirmation.