Relationship between Breast Cancer and Oral Contraceptive Use among Thai Premenopausal Women: a Case-Control Study

Background: Breast cancer (BC) is an important issue both in medicine and public health as it is the leading malignancy with high incidence and mortality among women worldwide. The objective of this research was to determine the associations of BC with oral contraceptive (OC) use among Thai premenopausal women (TPW). Materials and Methods: A case-control study was conducted among TPW attending the National Cancer Institute, with 257 cases and 257 controls in 2013-2014. Cases and controls were matched by age (± 5 years), residential area and duration of attendance. Data were collected with a questionnaire that comprised 2 sections: part 1 socio-demographic characteristics, and part 2 health risk behavior and reproductive factors. The obtained data were analyzed using descriptive and analytic statistics with a computerized statistical package. Results: The study participants were mainly 40-44 years old (60 %) with an average age of 39 years. The major BC type was invasive ductal carcinoma (91.8%). Multiple unconditional logistic regression analysis, controlling for possible confounding factors, revealed that TPW with OC use increased the risk of BC by a factor of over 3 times (ORadj=3.39, 95%CI =1.99-5.75). In addition, the greater the duration of OC, the greater the risk (ORadj 6-10 yrs=3.91, 95%CI = 1.99-7.64, ORadj >10 yrs=4.23, 95%CI = 2.05-8.71). Conclusions: From our findings, a surveillance system of cancer risk with OC use should be conducted, accompanied by an exercise promotion campaign among risk groups, providing information and counseling for physical exercise and physical activities, weight control and basic adjustment for a healthy lifestyle to reduce BC.