In late 2019, an interim analysis of a Phase I-II trial (NCT02332668) named KEYNOTE-051 has been published showing that Pembrolizumab has low antitumour activity in the majority of pediatric tumour types, and PD-L1 expression per se is not sufficient as a biomarker for response to treatment in pediatric patients [44]. This evidence concerns the gene CD274 and neoplasm.