ALK and neuroblastoma: Among 111 plasma/serum samples obtained from patients with NB at diagnosis, 20 patients were found to be positive for a single mutation and four patients were positive for both c.3522C > A and c.3824G > A. Mutant-to-wildtype ALK ratios ranged from 0.15% to 43.7%, likely reflecting different tumour burdens and disease stages within the cohort.