Tackling the adverse health effects of excess body fat in breast cancer: where does physical activity fit in?

Weight gain is commonly observed during and after breast cancer treatment due to chemotherapy and endocrine therapies, induced menopause, changes in metabolism and food intake and decreased physical activity. Systematic reviews show that women who are overweight or obese at diagnosis, and those who gain weight, have poorer breast cancer survival outcomes than women of a healthy weight, irrespective of menopausal status. Excess body weight after breast cancer also increases the risk of type 2 diabetes mellitus and CVD. The adverse impact of excess body weight on survival outcomes is clearly shown for women with oestrogen receptor-positive (ER+) breast cancer, which accounts for 70 % of all breast cancer cases. Higher body fat is thought to increase the risk of ER+ recurrence because of increased aromatase activity. However, this could be compounded by other risk factors, including abnormal insulin and adipokine metabolism, impaired anti-tumour immunity and chronic low-grade systemic inflammation. Observational evidence linking poorer survival outcomes with excess body fat and low physical activity in women recovering from early-stage curative-intent breast cancer treatment is reviewed, before reflecting on the proposed biological mechanisms. The issues and sensitivities surrounding exercise participation amongst overweight breast cancer patients is also discussed, before providing an overview of the co-design process involved in development of an intervention (support programme) with appropriate content, structure and delivery model to address the weight management challenges faced by overweight ER+ breast cancer patients.