Abstract

PIP: Previous studies have induced mammary tumors in rats and investigated the endocrine factors involved in maintaining the growth of these tumors. These studies have indicated that the pituitary plays a role in the estrogenic stimulation of rat mammary tumor growth. To further characterize the pituitary factor, rats with DMBA-induced mammary tumors that had regressed after oophorectomy and adrenalectomy were injected with ovine prolactin. Prolactin induced a reactivation of tumor growth, and this growth stopped and the tumors regressed promptly when prolactin was discontinued. These findings suggested that the effects of estradiol on mammary tumor growth may be mediated through the effects on pituitary prolactin secretion. Perphenazine, a tranquilizer with demonstrated mammotrophic and lactogenic effects, was shown to promote tumor growth in these rats and to stimulate the secretion of prolactin. Overall, the findings from this animal study suggest that prolactin may be the most significant hormone in maintaining mammary tumor growth. Although this process may also be applicable to human breast cancers, prolactin has not yet been isolated as a distinct hormone from human pituitaries. Isolation of human prolactin and the development of an immunoassay for this hormone are encouraged to facilitate the management of human mammary tumors. If prolactin is the decisive endocrine factor in human breast cancer, medical control of the secretion of this hormone could have major implications for the prevention as well as management of this disease.