B-cell acute lymphoblastic leukemia (Monarch Disease Ontology entry MONDO_0004947) is a neoplasm of lymphoblasts committed to the B-cell lineage, typically composed of small to medium-sized blast cells. When the neoplasm involves predominantly the bone marrow and the peripheral blood, it is called B acute lymphoblastic leukemia. When it involves nodal or extranodal sites, it is called B lymphoblastic lymphoma. (WHO, 2001). Also known as: B lymphoblastic leukemia/lymphoma, precursor B lymphoblastic leukemia/lymphoma, precursor B-lymphoblastic lymphoma/leukemia.