Risk factors for breast cancer in Turkish women with early pregnancies and long-lasting lactation--a case-control study.

A hospital-based case-control study was carried out among 504 women with breast cancer and 610 controls to analyse the risk factors for breast cancer in Turkey. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for each risk factor were obtained from logistic regression analysis. Risk factors for breast cancer were found to be long-term lactation (> or = 5 years versus never OR 0.31, 95% CI 0.12-0.79), young age at menarche (< 15 years versus > or = 15 OR 1.72, 95% CI 1.30-2.28), late age at first full-term pregnancy (> or = 30 versus < 20 OR 2.86, 95% CI 1.32-6.21), oral contraceptive use (ever versus never OR 1.51, 95% CI 1.10-2.08), positive family history (positive versus negative OR 2.81, 95% CI 1.35-5.82), and menstrual irregularity (yes versus no OR 1.61, 95% CI 1.05-2.49). The results of the present study will lead to a better understanding of the risk factors for breast cancer in a developing country.