Background: Breast cancer has been increased in developing countries, but there are limited data for breast cancer risk factors in these countries. To clarify the risk for breast cancer among the Turkish women, an university hospital based nested case-control study was conducted.
Methods: Between January 2000 and December 2006, a survey was prospectively conducted among women admitted to clinics of Istanbul Medical Faculty for examination and/or treatment by using a questionnaire. Therefore, characteristics of patients diagnosed with breast cancer (n = 1492) were compared with control cases (n = 2167) admitted to hospital for non-neoplastic, non-hormone related diseases.
Results: Breast cancer risk was found to be increased in women with age (> or = 50) [95% confidence interval (CI) 2.42-3.18], induced abortion (95% CI 1.13-1.53), age at first birth (> or = 35) (95% CI 1.62-5.77), body mass index (BMI > or = 25) (95% CI 1.27-1.68), and a positive family history (95% CI 1.11-1.92). However, decreased breast cancer risk was associated with the duration of education (> or = 13 years) (95% CI 0.62-0.81), presence of spontaneous abortion (95% CI 0.60-0.85), smoking (95% CI 0.61-0.85), breast feeding (95% CI 0.11-0.27), nulliparity (95% CI 0.92-0.98), hormone replacement therapy (HRT) (95% CI 0.26-0.47), and oral contraceptive use (95% CI 0.50-0.69). On multivariable logistic regression analysis, age (> or = 50) years (OR 2.61, 95% CI 2.20-3.11), induced abortion (OR 1.66, 95% CI 1.38-1.99), and oral contraceptive use (OR 0.60, 95% CI 0.48-0.74) were found to be associated with breast cancer risk as statistically significant independent factors.
Conclusion: These findings suggest that age and induced abortion were found to be significantly associated with increased breast cancer risk whereas oral contraceptive use was observed to be associated with decreased breast cancer risk among Turkish women in Istanbul.