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- Non-Hodgkin lymphoma (NHL) arises from the malignant proliferation of developing or mature B or T lymphocytes.
- Extent of disease is determined using the Murphy staging system:
- Stage I: single tumor (extranodal) or single nodal area, excluding mediastinum or abdomen
- Stage II: single tumor with regional nodal involvement, two or more tumors or nodal areas on the same side of the diaphragm, or a primary GI tract tumor (resected) with or without regional node involvement
- Stage III: tumors or lymph node (LN) areas on both sides of the diaphragm, any primary intrathoracic or extensive intra-abdominal disease (unresectable), or any paraspinal or epidural tumors
- Stage IV: bone marrow or CNS disease regardless of other sites; marrow involvement defined as 0.5–25% malignant cells
- Third most common childhood malignancy (~12% cancers in individuals <20 years of age in developed countries)
- Number of cases is increasing in adolescents and young adults.
- Male-to-female ratio: 3:1
- 10 to 20 cases per 1 million children per year
- Higher frequency of endemic Burkitt-type in equatorial African countries (10 to15 per 100,000 children <5 to 10 years)
- Incidence increases steadily with age; in children, usually seen in 2nd decade of life (unusual in those <3 years of age)
- Drugs: immunosuppressive therapy and diphenylhydantoin
- Radiation: atomic bomb survivors and ionizing radiation
- Viruses: Epstein-Barr virus (EBV) present in >95% of cases of endemic Burkitt versus <20% cases of sporadic; HIV
Genetic predisposition: increased risk in patients with immunologic defects (e.g., Bruton agammaglobulinemia, ataxia telangiectasia, Wiskott-Aldrich, severe combined immunodeficiency [SCID], X-linked lymphoproliferative syndrome [XLP])
- Unlike adults, low- and intermediate-grade NHL is uncommon in children (~7% of cases).
- NHL in children and adolescent can be divided into three major categories according to the National Cancer Institute (NCI):
- Mature B-cell NHL (Burkitt and Burkitt-like lymphoma, diffuse large B-cell lymphoma [DLBCL], primary mediastinal B-cell lymphoma)
- 50% of childhood NHL
- Express mature B-cell markers (CD20, surface immunoglobulin [Ig])
- Terminal deoxynucleotidyl transferase (TdT) negative
- Burkitt lymphoma has characteristic t(8;14), rarely t(8;22) or t(2;8); all chromosomal translocations involve the c-myc proto-oncogene.
- DLBCL usually of the germinal center B-cell phenotype. Unlike adults, the t(14:18) translocation is rare.
- Lymphoblastic lymphomas (LL)
- 30% of childhood NHL
- In children, 90% T-cell and 10% B-cell origin
- Morphologically identical to acute lymphoblastic leukemia. TdT positive; express early T (CD5, CD7, cytoplasmic CD3) or B (CD19, CD10) cell markers. Bone marrow involvement of >25% blasts is considered leukemia.
- Early thymic progenitor (ETP) subtype arises earlier in T-cell ontogeny. Most recent studies indicate it has a slower response to therapy but does not have a worse prognosis.
- Anaplastic large cell lymphoma (ALCL) (mature T-cell or null-cell lymphomas):
- 10% of childhood NHL
- Express CD30 (Ki-1)
- Contain chromosomal rearrangement involving the ALK gene (85% t2;5)
- Immunodeficiency-associated NHL usually of B-cell origin
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