Role of BMI and BMI-Adjusted Weight Loss in Cancer Cachexia
BMI plays an important role in assessing cancer cachexia because it helps us understand how serious a patient’s weight loss really is. The same percentage of weight loss has very different meanings depending on where a patient starts. For example, losing 3% of body weight is far more dangerous in someone who is already thin than in someone who is overweight. So BMI adds context that weight loss alone cannot provide.
However, BMI by itself is not perfect. In cancer patients, factors like edema, ascites, or sarcopenic obesity—where patients look normal or overweight but have very low muscle mass—can mask the true severity of tissue loss. That’s why BMI must be combined with measures of body composition using tools such as DEXA, BIA, or CT scans.
International consensus now diagnoses cancer cachexia using BMI plus unintentional weight loss and sarcopenia. Cachexia is defined as more than 5% weight loss, or more than 2% weight loss in patients with a BMI below 20, or any weight loss with proven muscle depletion.
To improve accuracy, we use the BMI-Adjusted Weight Loss Grading System, or WLGS. This system assigns patients to one of five grades by combining BMI and degree of weight loss. Each grade predicts survival: Grade 0 patients may live around 16 months, whereas Grade 4 patients—those with low BMI and substantial weight loss—have a median survival of only 4 to 6 months.
In practice, WLGS provides a powerful prognostic tool. The higher the grade, the worse the survival, functional status, and quality of life. Early identification helps clinicians intervene sooner with nutrition, exercise programs, and palliative support, tracking BMI and weight changes over time to monitor disease progression.