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BACKGROUND: Obesity has been reported as an adverse prognostic factor in breast cancer, but inconsistently, and under-treatment with chemotherapy may occur. We provide the first assessment of obesity and breast cancer outcomes in a population-based, multi-ethnic cohort of New Zealand patients treated with chemotherapy. METHODS: All 3536 women diagnosed with invasive breast cancer in the Waikato region of New Zealand from 2000-2014 were registered and followed until last follow-up in specialist or primary care, death or Dec 2014; median follow-up 4.1 years. For the 1049 patients receiving chemotherapy, mortality from breast cancer, other causes, and all causes, and rates of loco-regional and of distant recurrence, were assessed by body mass index (BMI), recorded after diagnosis, adjusting for other clinico-pathological and demographic factors by Cox regression. RESULTS: BMI was known for 98% (n=1049); 33% were overweight (BMI 25-29.9), 21% were obese (BMI 30-34.9), and 14% were very obese (BMI 35+). There were no significant associations between obesity and survival, after adjustment for demographic and clinical factors (hazard ratios, HR, for very obese compared to BMI 21-24, for breast cancer deaths 0.96 (0.56-1.67), and for all deaths 1.03 (0.63-1.67), respectively, and only small non-significant associations for loco-regional or metastatic recurrence rates (HR 1.17 and 1.33 respectively). Subgroup analyses by age, menopausal status, ethnicity, stage, post-surgical radiotherapy, mode of diagnosis, type of surgery, and receptor status, showed no associations. No associations were seen with BMI as a continuous variable. The results in all patients irrespective of treatment but with recorded BMI data (n=2296) showed similar results. CONCLUSIONS: In this population, obesity assessed post-diagnosis had no effect on survival or recurrence, based on 1049 patients with chemotherapy treatment with follow-up up to 14 years.

Original publication




Journal article


BMC Cancer

Publication Date





Body-mass index, Breast cancer, Obesity, Recurrence, Survival, Adult, Aged, Aged, 80 and over, Body Mass Index, Breast Neoplasms, Cohort Studies, Female, Humans, Middle Aged, Neoplasm Metastasis, Neoplasm Recurrence, Local, New Zealand, Obesity, Overweight, Survival Analysis, Young Adult