Outcome of adolescent patients with acute lymphoblastic leukaemia aged 10–14 years as compared with those aged 15–17 years: Long-term results of 1094 patients of the AIEOP-BFM ALL 2000 study

Background: Adolescents (aged 10–17 years) with acute lymphoblastic leukaemia (ALL) have unfavourable disease features and an inferior outcome when compared with younger children, but it is still unclear if differences in disease biology and prognosis exist between adolescents older or younger than 15 years. Methods: We retrospectively analysed outcomes of 1094 adolescents with ALL, aged 10–17 years, treated within the AIEOP-BFM ALL 2000 trial, overall and by the age groups 10–14 and 15–17 years. Findings: Compared with younger children (aged 1–9 years, n = 3647), adolescents had a statistically inferior 5-year event-free survival (EFS) [74.6% (1.3) vs. 84.4% (0.6)] and overall survival (OS) [83.4% (1.1) vs. 92.7% (0.4); p < 0.001]. Clinical and biological disease characteristics did not differ between the two subgroups of adolescents, including minimal residual disease (MRD) results during initial therapy, except for ETV6-RUNX1 frequency and gender. With a median follow-up of 8.8 years, the 5-year EFS and OS were 76.2% (1.5) and 84.9% (1.3), respectively, for those aged 10–14 years and 70.0% (2.8) and 78.8% (2.5) for those aged 15–17 years (p = 0.06; 0.05). There was no significant difference in the cumulative incidence of relapses [17.8% (1.4) and 18.3% (2.4); p = 0.98], while the incidence of treatment-related deaths as a first event was 2.6% (0.6) versus 7.4% (1.6) (p < 0.001) with, in particular, a higher incidence in the high-risk arm. Interpretation: Further prospective studies and biological investigations are required to define optimal treatment for adolescents, in particular for those aged 15–17 years. Newer agents (immunotherapy, targeted therapy) in early treatment phases of patients at higher risk of treatment failure could replace most toxic treatment elements, with the aim of reducing both toxicity and the risk of relapses.