[Can breast cancer be prevented?]

Abstract

More than six-fold variation in incidence between countries, an increasing incidence among immigrants to high incidence areas, and a general increase in the incidence of breast cancer within countries, are factors which suggest a potential for prevention. Reproductive factors such as early menarche, late age at first full term birth, nulliparity, and late age at menopause increase risk of breast cancer, but manipulation of any one of these factors does not seem to be a realistic preventive tool. Nevertheless, the future possibility of using tamoxifen as a chemopreventive agent against breast cancer is discussed, particularly in relation to women at increased risk due to familial clustering. Alcohol consumption by young women, and overweight among postmenopausal women may also increase the incidence of breast cancer. Consequently, reduced alcohol intake by young women, and weight reduction among overweight women after menopause may reduce the risk of breast cancer.

PIP: In 1980, there were 570,000 cases of breast cancer in the world. In Norway, there are an average of 2000 new cases per year, and incidence had increased 50% from 1955 to 1984. About 40% of those afflicted die of the disease. Environmental, age, and reproductive factors seem to be implicated in its genesis. The rate increased almost fivefold in the course of a generation among Polish people who migrated to California from low incidence areas. It doubled among Chinese and Japanese who moved to California. The rate increases sharply up to age 50, then it levels off, thus early menopause is protective. Ovarial hormones (estrogen and progesterone) play a role in the development of preclinical tumors. Younger age at first delivery offers protection, but women who give birth to their first child after age 35 face a higher risk than nulliparas. Women with early menarche, which can be delayed by a lower caloric intake and vigorous physical activity, also face a heightened risk. Before menopause, overweight women are relatively protected, but the reverse is true after age 60. The consumption of animal fat is another risk factor, although a US study that involved 90,000 nurses did not bear this out. The Japanese increased their intake of animal fat from 10-25% from 1955-1975 without a corresponding increase in the rate of breast cancer. A vegetarian diet is nonprotective. Even the moderate consumption of alcohol increases the risk by 40% for women aged 15-30. Long-term use of oral contraceptives before birth of the first child up to age 35 increases the risk. Tamoxifen has protected women with a familial history of breast cancer who face a 3-5 fold higher risk. After menopause, its estrogenic properties promote the risk. Tamoxifen has an antitumor effect that can treat tumors clinically which are not manifested; it also lowers LDL (low density lipoprotein) and increases HDL (high density lipoprotein) cholesterol.