Obesity and postmenopausal breast cancer: impact on risk, tumour stage and survival in an Irish population.

Abstract

Abstract Abstract #6089 Background 
 The evidence that obesity adversely affects women's health is overwhelming and indisputable. The risk of postmenopausal breast cancer increases with obesity. Furthermore it is reported that obesity is associated with poorer prognosis of breast cancer.
 Objective
 To assess the relationship between obesity and postmenopausal breast cancer by examining the incidence, tumour size, pathological stage, axillary nodal involvement and survival in an Irish population.
 Design & Setting
 A retrospective case control study was undertaken in 200 patients presenting to a tertiary centre between 1998-2006. Data were compared to 519 healthy female controls. Multivariate logistic regression models were used to calculate the odds ratio (OR) of developing postmenopausal cancer according to body mass index (BMI), as well as the impact BMI has on tumour size, nodal involvement, pathological stage and survival. Actuarial survival was calculated from date of diagnosis by the Kaplein-Meier method and comparisons between the groups were made by the log rank test.
 Results
 Postmenopausal breast cancer patients were significantly heavier than age matched controls with 65% being overweight or obese versus 54% of controls (p=0.030). A dose dependent relationship existed between BMI and postmenopausal breast cancer incidence. The adjusted odds ratio was 2.2 (95%CI 1.3-3.7) for individuals in the highest BMI quartile compared to the lowest BMI quartile (P=0.002). Using common cut-offs for BMI, obese patients had double the risk of postmenopausal breast cancer compared to normal weight patients OR 2.04 (95%CI 1.3-3.3; p=0.004). There was no difference in symptomatic detection, assessment or treatment of breast cancer, however operative times were significantly longer for obese patients (P=0.05). Obesity was associated with larger tumours (P= 0.002) and a later stage of disease at presentation (P=0.026) but not with axillary nodal involvement (P=0.332). Median and overall survivals were equivalent (P=0.172) when comparing obese to non obese.
 Conclusion
 Obese women are twice as likely to get postmenopausal breast cancer compared to normal weight women. Understanding why obese women have a higher breast cancer incidence may lead to more effective breast cancer prevention and treatment interventions. Obesity is a preventable risk factor for breast cancer and given the high and increasing prevalence of obesity in Ireland, obesity needs to be addressed on a national level with targeted lifestyle treatment programs. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6089.