Guidelines on Diagnosis and Treatment of Malignant Lymphomas

Precursor T Cell Neoplasms
PRECURSOR T LYMPHOBLASTIC
LEUKAEMIA/LYMPHOBLASTIC
LYMPHOMA
Definition and Incidence
Precursor T lymphoblastic leukaemia (T-ALL)/lymphoblastic
lymphoma (T-LBL) is a neoplasm of T-precursor lymphoblasts
with an immature immunophenotype. Patients typically present
with a mediastinal mass and frequent marrow involvement. The
condition accounts for 15% of childhood and 25% of adult ALL.
Adolescent males are the most commonly affected group.
ICD-O Code Leukaemia: 9837/3
Lymphoma: 9729/3
Clinical Presentation
Patients usually present with short history of increasing dyspnoea
secondary to a rapidly-evolving mediastinal mass associated with
a high leukocyte count. Other sites involved include lymph nodes,
liver, spleen, skin, Waldeyer’s ring, and gonads.
Pathology
The lymph node architecture is effaced by a monomorphic
population of lymphoblasts. The lymphoblasts are medium sized
with a high nuclear–cytoplasmic ratio, irregular nuclei, fine
chromatin and inconspicuous nucleoli.
Immunophenotype
T-ALL/T-LBL is always TdT positive. Pan T markers including
CD3, 4, 5 ,7 and 8 are variably expressed with cytoplasmic
CD3 and CD7 most commonly expressed. Co-expression
of CD4 and CD8 may occur.
Genetics
One third of T-ALL/T-LBL have translocations involving the
T-Cell Receptor (TCR) loci at 14q11 (TCR alpha and delta),
7q35 (TCR beta) and 7p14 (TCR gamma). Translocation partner
chromosomes include 8q24 (MYC), 1p32 (TAL1) and others.
25% of cases have TAL1 dysregulation either by translocation or
microscopic deletion. More than 30% have del(9p) resulting in
loss of the tumour suppressor gene CDKN2A, an inhibitor of the
cyclin-dependent kinase CDK4.
Investigations
Generic see page 2
Specific
BMA to be assessed by morphology and
immunophenotype. If the marrow is
morphologically involved, cytogenetics
are mandatory.
CSF analysis to exclude meningeal disease
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