Malignant pleural mesothelioma (MPM) is an incurable cancer with limited survival and treatment options. Optimising and maintaining quality of life and daily physical activity are key goals of patient care. In our research, we have found high rates of malnutrition (38%) and low muscle mass (54%), even amongst those who were overweight and obese and with a good performance status. Malnutrition was associated with poorer cancer specific health-related quality of life whilst low muscle mass was associated with lower accelerometer-measured physical activity levels. Prospectively, there was a significant positive correlation between changes in weight and changes in quality of life and physical activity levels. These results suggest that weight maintenance or gain could be integral to optimal supportive care in MPM. Interventions that address weight loss and low muscle mass, such as resistance exercise and nutritional support should be tested in MPM. However, to be effective, interventions must consider the complicated aetiology of malnutrition and low muscle mass. Outcome measures for interventions also need to be sensitive to change. Using data from our prospective, observational study of patients with MPM, this presentation will discuss the challenges associated with addressing malnutrition and low muscle mass in this population.