Female sex hormones increase the risk of breast cancer
Vatten, L.
Tidsskrift for den Norske Laegeforening Tidsskrift for Praktisk Medicin Ny Raekke 118(19): 2969-2974
1998
ISSN/ISBN: 0029-2001 PMID: 9748837 Document Number: 986
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.
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