Existing definitions of clinically important weight loss in patients with cancer do not specifically address weight loss in patients who are obese at presentation. This review explores the clinical impact of weight loss and depletion of the skeletal muscle mass (i.e., criteria defining cancer cachexia), in patients with obesity.

Overweight and obese BMI values are shown by many recent studies to pose a survival advantage in patients with cancers of advanced stage, when compared with BMI in normal and underweight ranges. The classification of cancer-associated weight loss has evolved, and current grading schemes evaluate the impact of weight across the range of BMI values.

Weight loss is associated with mortality in patients with BMI more than 30 kg/m 2 , however this is to a much lesser degree than in patients with lower BMI values. Diagnostic imaging permits the precise assessment of skeletal muscle index (SMI) in patients with cancer, and it has been clearly shown that while usually quite muscular, obese patients can have profound muscle depletion (i.e., sarcopenia), independent of the presence of weight loss.

Muscle depletion associates strongly with mortality in obese patients, as well as with complications of cancer surgery and systemic therapy. It would seem contradictory to diagnose concurrent obesity and cachexia, as these terms represent opposite ends of the weight spectrum.

Weight loss can occur in anyone with cancer, however its priority for clinical management may be lesser in obese versus low body weight individuals. Sarcopenic obesity is strongly associated with a poor clinical outcome and deserves further research, diagnosis in clinical practice, and new strategies for mitigation.