A case-control study of risk factors for breast cancer in Brazil, 1978-1987

There are still controversies regarding the role of many risk factors assessed for breast cancer worldwide. In Brazil, it represents a major cause of death among women but yet few analytical studies have been published to date.

The association of selected factors with breast cancer was assessed in a case-control study of 300 women, aged 25-75 years, treated at the Federal University Hospital, Belo Horizonte, Brazil, from 1978 to 1987. In all, 300 cases with diagnosed breast carcinoma were compared with 600 controls matched on age and date of diagnosis. Socio-economic, demographic and reproductive factors were analysed.

Multiple logistic regression analysis showed the following factors to be independently associated with increased risk of breast cancer: a) monthly family income (odds ratio [OR] = 1.69, 95% confidence interval [CI]: 1.18-2.42); b) being a housewife (OR = 2.86, 95% CI: 1.83-4.47; c) parity of less than six deliveries and nulliparous women (OR = 5.06, 95% CI: 3.01-8.52 and OR = 2.42, CI: 1.64-3.59, respectively); d) history of breast cancer among first degree female relatives (OR = 9.35, 95% CI: 3.22-27.14); and e) oral contraceptive use (OR = 1.81, 95% CI: 1.15-2.85). Irregular menstrual cycle (OR = 0.44, 95% CI: 0.25-0.75) was associated with breast cancer as a protective effect.

The study has confirmed most risk/protective factors previously demonstrated elsewhere in the world and provides clear documentation of breast cancer epidemiology in Brazil.