Introduction
Childhood brain tumor survivors (CBTS) are at increased risk for developing obesity which may negatively influence cardiometabolic health in adulthood. We aimed to study the prevalence and risk factors for significant weight gain, overweight or obesity in a large cohort of non-craniopharyngioma and non-pituitary CBTS.

Methods
This nationwide study cohort consisted of 718 CBTS. All CBTS who were diagnosed between 2002 and 2012, survived ≥ two years after diagnosis and of whom BMI development was known were included. Patients with craniopharyngioma or a pituitary gland tumor had been excluded. Multivariate logistic regression was used to study associations between tumor-, or treatment-related variables and the prevalence of weight gain (BMI change ≥ +2.0 standard deviation score (SDS), overweight or obesity at follow-up.

Results
661 CBTS (46.1% female) were included, with a mean age at diagnosis of 7.78 years and a mean age at follow-up of 15.14 years. Of all CBTS, 14.5 % showed significant weight gain between diagnosis and last moment of follow-up. Risk factors for significant weight gain were the presence of hydrocephalus at diagnosis (OR 1.63 CI 95% 1.04 – 2.56), the presence of central diabetes insipidus or central precocious puberty (CPP) at follow-up (OR 3.43 95% CI 1.36 – 8.63), and longer follow-up time (OR 1.10 95% CI 1.02 – 1.19).
In total, 20.3% of the CBTS were classified as overweight and 8.5% as obese at follow-up. BMI SDS at diagnosis (OR 1.99, CI 95% 1.69 – 2.34) and having CPP or DI at follow-up (OR 3.3 CI 95% 1.29 – 8.39) were both significantly associated with overweight or obesity at follow-up.

Conclusion
The prevalence of significant weight gain, overweight and obesity in CBTS is high, in a non-craniopharyngioma and non-pituitary cohort. Children who present with a high BMI at diagnosis, hydrocephalus at diagnosis, or who develop DI or CPP during follow-up are at serious risk for weight gain and should be counseled at an early stage aiming to reduce BMI and cardiometabolic risk in adulthood.