Despite being the most prevalent cancer among children, over 90% of pediatric acute lymphoblastic leukemia (ALL) cases are cured in most developed countries.1 This has largely been attributed to the introduction of risk stratification protocols and risk-directed therapies.2 However, there remains heterogeneity in treatment responses within risk groups which suggests the need for risk stratification to be further refined.2 The predictive potential of CD9, a tetraspanin family protein that regulates cell motility, adhesion and signaling, in survival outcomes of patients with childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL) was previously highlighted in a local single-center investigational study.3 Thereafter, researchers from The Chinese University of Hong Kong (CUHK) and clinicians in the Hong Kong Children’s Hospital conducted a nationwide, multicenter, retrospective study to validate clinical performance of CD9 as a prognostic biomarker in childhood ALL.2