Lymphoblastic Lymphoma

Acute leukemia accounts for up to 30% of all childhood malignancies. Acute lymphoblastic leukemia (ALL)/lymphoblastic lymphoma (LBL) is a clonal hematopoietic stem cell disorder of B or T cell origin. The World Health Organization (WHO) 2017 classification system categorizes these disease entities under precursor lymphoid neoplasm. The WHO 2017 classification of precursor lymphoid neoplasm includes 4 distinct entities: B-ALL/LBL not otherwise specified (NOS); B-ALL/LBL with recurrent genetic abnormalities; T-ALL/LBL; and NK-ALL/LBL. Lymphoblasts are the characteristic cells of this disease entity. The lymphoblasts are usually small to medium-sized with scant cytoplasm, moderately condensed to dispersed chromatin, and inconspicuous nucleoli. The lymphoblasts traditionally involve the bone marrow (BM) and/or blood in ALL and involve the lymph nodes in LBL. The diagnosis is of ALL is rendered when the blast count exceeds 20%. Occasionally, patients present with primary lymph node involvement of nodal or extranodal sites (LBL). Sometimes, there is an overlap between ALL and LBL, and it has been widely accepted to render a combined diagnosis. NK-ALL/LBL is currently a provisional entity in the WHO 2017 classification. It is a rare entity, and diagnosis often overlaps with T-ALL/LBL. ALL is one of the earliest neoplasms where chemotherapeutic treatment showed a favorable outcome. It has also been one of the earliest neoplastic disease entities where the understanding of biology has led to direct changes in the management of patients.