Body mass index (BMI): association with clinicopathological factors and outcome of women with newly diagnosed breast cancer in New Zealand.

AIMS: To identify associations of obesity with breast cancer and its outcome in a New Zealand population, including those treated with adjuvant chemotherapy.

METHODS: Data was collated from four regional Breast Cancer Registers, Auckland, Waikato, Wellington and Christchurch, for all women with newly diagnosed breast cancer, with weight and height recorded. Associations of body mass index (BMI) with patient and tumour characteristics, and all-cause mortality were determined.

RESULTS: BMI was available for 5,458 new breast cancers, 27% of all registered. BMI was normal (18.5-24.9kg/m2) for 32.7%, overweight (25-29.9kg/m2) 31.1%, obese (>30kg/m2) 34.9% and 1.3% underweight (<18.5kg/m2). Median age was 55 years. Higher BMI was associated with non-European ethnicity, post-menopausal status, screen-detection, older age and tumours with higher grade, greater size and positive progesterone receptors. Mean survival for women younger than 56 years was 18.0 years for normal BMI and 14.8 years for BMI >35 (p=0.055, Log-rank). Women younger than 56 years treated with adjuvant chemotherapy had lower survival if obese compared with normal BMI (p=0.055, Log-rank).

CONCLUSIONS: High BMI was associated with larger tumours, of higher grade, progesterone receptor positive and post-menopausal status. Obese pre-menopausal women treated with adjuvant chemotherapy had a trend to poorer outcome.