A 26-year-old man with the main complaint of “bleeding gums, sore throat, petechiae, and melena” was diagnosed with acute lymphoblastic leukemia (pro-B lymphocyte, BCR-ABL chimeric gene-positive) by bone marrow biopsy, flow cytometry analysis of B cells, and genetic analysis, when marked leukocytosis (94.24 × 109/L), thrombocytopenia (31 × 109 /L), and anemia (103 g/L) were present. The gene discussed is BCR; the disease is acute lymphoblastic leukemia.