Background: Breast cancer is a majo

Background: Breast cancer is a major public health problem and is the most common
form of invasive cancer in women worldwide. In order to discover the cause of breast cancer in
women and reduce its incidence, it is important to determine the factors associated with the disease.
Objective: To identify factors associated with the incidence of breast cancer in women.
Methods: Data were provided by the Khon Kean Cohort Study, which is operated by the
Cancer Unit of the Faculty of Medicine, Khon Kean University. According to reports supplied by
the provincial cancer registry, there were 70 cases of breast cancer amongst the 11,414 women
aged 30-69 years, who were recruited as participants in the cohort study during the period 1990-2001.
The medical records showed that the diagnosis had been confirmed by physical and histological
examinations. The study population was monitored until 31 December, 2011. To identify factors
associated with the incidence of breast cancer, hazard ratios and 95% CIs were computed using
the Cox proportional hazard model.
Results: The study population of 11, 414 provided a total observation time of 157, 200
person-years. Women with a history of using hormone contraception for periods of five or more
years had a 1.44 times greater risk of breast cancer than a reference group, who had used this
form of contraception for periods of less than five years (HRadj: 1.44, 95% CI: 1.22 to 3.45).
Women using hormone contraception for 5-9 years and those with a history of 10 or more years
of use had a 2.59 and a 1.82 times greater risk, respectively, than the reference group (HRadj: 2.59,
95% CI: 1.11 to 6.06 and 1.82 HRadj: 1.82, 95% CI: 1.07 to 4.37).
Conclusion: This study suggests that the use and duration of use of hormonal contraceptives
(the pill), are positively associated with the incidence of breast cancer in women. To prevent
breast cancer it is important for women to have greater awareness of the risk factors. Public health
services also need to informed so they can promote safe methods of family planning.