Studies of Prolactin Receptors and the Possible Proliferative Role of Prolactin and Other Pituitary Factors in Human Breast Tumor Cells

Abstract

Prolactin and estrogen play key roles in influencing the growth behaviour of experimental breast tumors of rodents (7), (11), (17), (23), (43). However, the involvements of these two hormones, especially that of prolactin, in the tumorigenesis of the human breast, is still unclear (20). Whether or not trophic factors other than these two hormones are also important in growth regulation of breast cancer remains to be elucidated. Clinical investigations have indicated that pituitary hormones are important in the etiology of human breast cancer although the identity of the pituitary factors have not been elucidated. In view of the important role that prolactin plays in the tumorigenesis of rodent breast cancer, the notion that this hormone may be involved in the etiology of human breast cancer has been formulated (23). Evidence, mainly derived from clinical observations, has so far failed to establish an importance of prolactin in the breast disease of man (20). However, studies with human breast tumor biopsies maintained in organ culture using a pentose pathway histochemical effect suggest that some tumors show some form of prolactin dependency (26). Further, it has been reported that human breast biopsies maintained in organ culture (42) or transplanted in athymic nude mice (16) respond to prolactin and placental lactogen with an increase in DNA synthesis. One of the recent advances in human breast cancer research has been the development of a considerable number of cell lines derived from breast cancer specimens (4). The use of these human breast cancer cell lines maintained in tissue culture has provided new insight into the hormonal control of breast cancer in man. The proliferation of some human breast tumor cell lines in culture are affected by hormones such as insulin (1), (22) and epidermal growth factor (4).