Introduction
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) classified by the World Health Organization in March 2020 [1], has become an outbreak around the world. However, compared to adults, the coronavirus disease 2019 (COVID-19) may less impact the pediatric population with most having a milder symptoms [2]. In general, COVID-19 in children very less than adults, haematological disease following SARS-CoV-2 infection in pediatric patients is rare. Here, we reported a pediatric case who developed B cell acute lymphoblastic leukemia (B-ALL) following mild SARS-CoV-2 infection. A Chinese family was diagnosed as mild type of COVID-19 infection in Belarus. Without any treatment, SARS-CoV-2 RNA and COVID-19-specific antibodies IgM were negative after two weeks. But the boy in this family showed bone pain and pancytopenia after nineteen days from diagnosed COVID-19. With basic supportive treatment, his symptoms and hemograms returned to normal. Previous symptoms appeared again with significantly elevated white blood cells. As well, blast cells also experienced transient decline and increased again without any treatment. For further diagnosis and treatment, they were back to China. Eventually laboratory findings confirmed B-ALL in Beijing Children’s hospital.