Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (338 page)

   Definition

T-ALL is a neoplasm of lymphoblasts committed to the T-cell lineage. The term lymphoma is preferred to leukemia when the presenting manifestation is a tumor, rather than peripheral blood involvement. The incidence of T-ALL in children with ALL ranges between 10% and 15% and in adults between 20% and 25%.

   Who Should Be Suspected?

Presentation is similar as for B-ALL (see p. 389), but there is more predominant extramedullary involvement, including frequent CNS and anterior mediastinal thymic masses.

   Laboratory Findings

   CBC: (see B-ALL at p. 389, but note higher leukocytosis at presentation).

   Immunophenotype: CD3 is T-lineage specific. The lymphoblasts are TdT positive and express CD1a, CD2, CD4, CD5, CD7, and CD8 to variable degrees. CD10 may also be positive.

   Molecular genetics: Clonal rearrangement of the T-cell receptor gene (TCR) is almost always present.

   Cytogenetics: Abnormal karyotypes are present in 50–70% of cases. The most common recurrent abnormality involves the α and Δ TCR loci at 14q11.2.

Suggested Reading

Borowitz MJ, Chan JKC. T lymphoblastic leukaemia/lymphoma. In:
WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues
, 4th ed. Lyon, France: International Agency for Research on Cancer; 2008:176–178.

   
CHRONIC LEUKEMIAS
^‡

CHRONIC MYELOGENOUS LEUKEMIA

[See Myeloproliferative Neoplasms]

CHRONIC EOSINOPHILIC LEUKEMIA (CEL) AND HYPEREOSINOPHILIC (HES) SYNDROME*

   Definition

CEL is a rare clonal myeloproliferative disease characterized by the overproduction of eosinophils. It must be distinguished from the HES, reactive eosinophilia, or other leukemias with predominant eosinophilia. It may undergo blastic transformation. HES is defined as persistent (>6 months’ duration) eosinophilia of >1,500 eosinophils/mL with no demonstrable disease that could cause eosinophilia, no abnormal T-cell population, and no evidence of another clonal myeloid disorder. It leads to end-organ damage because of the proinflammatory role of eosinophils; any organ may be involved. If untreated, HES may be fatal.

   Persistent peripheral blood eosinophilia (≥1,500/μL).

   Myeloblasts <20% in peripheral blood or bone marrow, and there are no cytogenetic features diagnostic of AML.

   No evidence of other myeloproliferative neoplasms or MDS/MPN.