Overweight may be associated with favorable outcome whereas tumor cachexia may be associated with worse outcome in patients with metastatic cancer. Here we evaluate the association of abnormal body mass index and weight change with outcome in patients with brain metastasis.

Patients with a diagnosis of brain metastasis treated at the University Hospital Zurich (n = 703) were assessed for associations of body mass index, weight change, comorbidities and survival.

Compared with patients with normal body mass index of 18.5-24.9 kg/m² and a median overall survival of 9 months (95% confidence interval 7.5-10.5), overall survival was inferior in patients with body mass index < 18.5 kg/m² (overall survival 6 months, 95% confidence interval 1.6-10.3, p = 0.04), but superior in patients with body mass index > 25 kg/m² (overall survival 13 months, 95% confidence interval 11.0-15.0; p = 0.033). We report a median relative weight loss of 5% within the first 6 months of diagnosis of brain metastasis (95% confidence interval 3.3-6.5), and reduction exceeding the median was associated with an unfavorable outcome (weight loss < 5% 22.0 months, 95% confidence interval 19.2-24.8; weight loss > 5% 14.0 months, 95% confidence interval 11.9-16.).

High body mass index is associated with better, and underweight with worse outcome in patients with brain metastasis. Conversely, weight loss above median may predict poor outcome. Future studies need to address whether vigorous treatment of tumor cachexia, e.g. by specific nutrition management, might improve outcome of patients with brain metastasis. In contrast, regimens associated with weight loss such as ketogenic diet may be detrimental.