Etiologic factors in cancer of the breast in humans.

This article details newer information on endocrine viral genetic and other etiologic factors in cancer of the breast considered pertinent from a surgeons point of view. The role of estrogens and other ovarian hormones has not been confirmed. The early peak age group for breast cancer (45-49 years) has been thought to be related to ovarian dysfunction. The protective effect of pregnancy is ascribed to the antagonistic effect of the greatly increased amount of estriol against estradiol. Prolonged lactation is no longer considered to give any protection. Carcinoma of the male breast has been reported in patients taking estrogens for prostate cancer; however such tumors may be metastases. Large doses of estrogen sometimes are effective in treating premonopausal women whereas small doses may enhance the cancer. Progesterone and synthetic progestational agents have shown immunosuppressive action against virus infections in animals; thyroid hormones may have an effect but it is uncertain; adrenal gland dysfunction may produce a hormonal milieu favorable to breast cancer long before the cancer develops. Corticosteroids affect susceptibility to infection as well as to malignant tumor induction in animals. Androg ens have been shown to have some retarding effect on disseminated cancers but the mechanism is unknown. The role of pituitary hormones and oral contraceptives is not yet known. Several strains of mammary tumor virus in mice have been demonstrated different methods of transmission have been shown for each strain and all virus-induced tumors are antigenically identical to the inducing virus. (All viruses identified in breast tumor are ribonucleic acid B-particle types.) An immunization premenopausal using large doses of purified preparations of the viruses has developed considerable protection of mice through development of strong antiviral agents called interferons. Such substances have potential immunoprophylaxis value for humans. The significance of viruses in human cancer of the breast has not been established with certainty as it has in animals. Many of the etiologic factors in humans may be genetic in origin. Familial risk has been shown to be inherited through either parent line and develops in younger persons in subsequent generations. Trauma to the breast is not of etiological significance but may aggravate preexisting cancer. Repeated radiation exposure high-fat diets and metabolic activity of intestinal bacteria have also been implicated.