The effect of body mass index and oestrogen receptor level on survival of breast cancer patients

Background Epidemiological studies have demonstrated that obesity and low oestrogen receptor level adversely affect survival from breast cancer. Few studies have examined the joint effects of these variables. Methods. A cohort study was conducted in which 1169 breast cancer patients from the Northern Alberta Breast Cancer Registry were followed for an average of 4.4 years. A number of variables related to breast cancer incidence and prognosis were studied. Body mass index (BMI) was used as a proxy measure of obesity, Results. A Cox regression analysis resulted in a final model with terms for size of tumour, number of positive axillary nodes, oestrogen receptor level, BMI, and age at diagnosis, plus an interaction term for node status and BMI, Having relatively less oestrogen receptor increased the hazard ratio by 1.8 (95% CI : 1.4-2.3); for women with no positive nodes, being in the highest quartile of BMI increased the hazard ratio by 2.5 (95% CI : 1.2-5.2) compared to the lowest quartile. Conclusions. BMI and oestrogen receptor level independently influence survival from breast cancer, but BMI affects survival only in patients with no positive axillary nodes.