Obesity is a well-established risk factor for cancer, having now been associated with the incidence of 10 different types of cancers. In adults who have been diagnosed with cancer, particularly those with high relative survival rates (e.g. breast, prostate, endometrial, colorectal), evidence suggests that obesity is associated with an increased risk of disease-specific mortality and/or all-cause mortality, compared to those with a healthy body weight. The mechanisms underlying the link between obesity and cancer progression are not well understood, but likely involves a complex relationship of multiple inter-related pathways. Body composition (i.e. lean body mass/fat mass) rather than weight or body mass index (BMI) per se, may be more important, but has rarely been examined in epidemiological studies. This presentation will provide an overview of the evidence on obesity and weight loss in cancer survivors, with a specific focus on breast cancer survivors. While the evidence is currently lacking on whether intentional weight (adiposity) loss, healthy diet and increased physical activity can improve cancer survival, weight loss, diet and physical activity have been shown to have important benefits on improving quality of life and reducing treatment-related side-effects. Given the growing numbers of cancer survivors in Australia, interventions to improve their health and well being are needed to improve quality of life and reduce health care costs.