The incidence of breast cancer in women in increasing, partly due to changes in age distribution in the population, and partly due to a real increase in risk. Changes in family patterns may, to some extent, explain the increased risk since giving birth to a first child late in life and bearing few children both increase the risk of breast cancer. The influence of female sex steroids on the breast plays a central role, but the biological mechanism is not clearly understood. There is a certain amount of risk involved in using hormonal medication (oral contraceptives or postmenopausal hormone replacement), but on ceasing to take the medication, risk will revert to the expected rate within a few years. Future epidemiological research on breast cancer will concentrate on events occurring during hormonally potent phases of life, such as growth and development during the fetal period, and sexual and somatic maturation during adolescence. Until now only modest interest has been shown in researching these two particular phases, but both may be important for the natural course of breast cancer.
PIP: The incidence of breast cancer is on the rise in women, partly owing to changes in the age distribution in the general population and also because of a genuine increase in risk. Women who give birth to their first child at the age of 30 years face double the risk of women who give birth at the age of 19. Women who have 1 child also have double the risk compared to women who have 4 children. Menopause at the age of 55 also doubles the risk compared to menopause at the age of 45. The participation of women in the labor market also has implications owing to later childbearing and giving birth to fewer children. It is a paradoxical element that pregnancy causes a temporary increase in the risk for breast cancer followed by a lifelong protection against it. The 1994 US Nurses' Health Study followed up 90,000 nurses for 14 years and found 2,000 new cases of breast cancer among them. Another study in Oxford, England, reanalyzed the data of 54 epidemiological studies involving 53,297 women with breast cancer and 100,239 women without breast cancer. Women using oral contraceptives (OCs) were found to have a 24% higher risk for breast cancer compared to women who never used OCs. Women who received hormone replacement therapy also had a 35% higher relative risk for breast cancer compared to women who never used such medication. Furthermore, both early menarche and sudden body growth in puberty were associated with increased later risk. Strong positive association was also found between higher birth weight and breast cancer. Women who were born prematurely also had a distinctly increased risk, while preeclampsia reduced the risk owing to the lower estrogen concentration in utero.