In line with the previous data, 23 of the 84 (27%) children with ALCL were found to have monoallelic mutations in one of three genes: 21 patients (25%) carried a total of 10 different mutations of PRF1, 2 additional patients had missense mutations of the UNC13D gene, but no mutations were found in the gene SH2D1A. The observation that PRF1 is involved in a quarter of patients with ALCL suggests a correlation between insufficient cellular cytotoxicity and development of ALCL. Here, PRF1 is linked to anaplastic large cell lymphoma.