Concordant ETV6::RUNX1-positive acute lymphoblastic leukemia in monozygotic twins: a case report and review of the literature

This case report describes a case of monozygotic twins with acute lymphoblastic leukemia (ALL). Patient A, aged 1 year and 6 months, was admitted due to a 2-day fever. His brother, Patient B, aged 1 year and 9 months, was admitted for a 1-day fever and abnormal blood findings. Both were diagnosed with ALL and both tested positive for the ETV6::RUNX1 fusion gene. The twins underwent two years of chemotherapy according to the CCLG-ALL-2018 protocol. During treatment, both achieved complete remission. Following treatment completion, they have remained in continuous complete remission for over 2 years of follow-up. This case provides clinical evidence supporting the "in utero origin" and "two-hit" hypotheses in pediatric ALL.