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Reproductive factors and colon cancers
R K Peters1, M C Pike, W W Chang
1Department of Preventive Medicine, University of Southern California School of Medicine, Los Angeles 90033.
British Journal of Cancer
|May 1, 1990
Summary
Pregnancy offers protection against colon cancer, with risk decreasing with more pregnancies up to four. However, the relationship is U-shaped, increasing with additional pregnancies, particularly in the distal colon.
Area of Science:
- Epidemiology
- Gastroenterology
- Reproductive Health
Background:
- Colon cancer incidence rates show a crossover in women before age 55, suggesting reproductive factors may play a role.
- Reproductive and menstrual factors are hypothesized to influence age-specific colon cancer incidence rates, particularly in the distal colon.
Purpose of the Study:
- To investigate the association between reproductive factors and colon cancer risk in women.
- To examine the impact of pregnancy history on the incidence of colon adenocarcinoma.
Main Methods:
- A population-based case-control study was conducted with 327 white women diagnosed with colon adenocarcinoma.
- Controls were matched for age, race, and neighborhood. Data on reproductive history and other risk factors were collected and analyzed.
Main Results:
- Ever having been pregnant was found to be protective against colon cancer (RR = 0.56).
- A U-shaped relationship was observed between the number of pregnancies and colon cancer risk, with risk decreasing up to four pregnancies and then increasing.
- This U-shaped association was more pronounced for distal colon cancers and was not influenced by age at menarche or exogenous estrogen use.
Conclusions:
- The pregnancy effect fully explains the observed crossover in incidence rates in the distal colon.
- Competing factors may contribute to the U-shaped relationship between pregnancy and colon cancer risk, with some protective effects and others increasing risk with more pregnancies.