Acute lymphoblastic leukaemia (ALL) and lymphoblastic lymphoma are two closely related conditions. In the French-American-British (FAB) classification, which largely predated immunophenotyping, ALL was categorized according to morphology, as L1, L2 and L3. In the World Health Organization (WHO) classification ALL and lymphoblastic lymphoma are grouped together as precursor B-cell and precursor T-cell neoplasms.
In cases of ALL occurring in infants the leukaemia often has its origin in intra-uterine life and in childhood cases there may be a pre-leukaemic clone already present at the time of birth [1, 2].
The more common cases of B-lineage ALL show a peak incidence between the ages of 2 and 10 years. This child hood peak is particularly characteristic of developed countries. T-lineage cases tend to be older and show a male predominance.
Clinical features differ between lymphoblastic lymphoma and ALL and differ somewhat between B- and T-lineage cases. Overall, presentation as lymphoma is much less common than presentation as leukaemia. T-lineage cases are more likely than B-lineage to present as lymphoma. About three-quarters of cases are B-lineage and about one-quarter T-lineage.
Patients with ALL present either with clinical features of bone marrow failure (pallor and bruising) or with clinical features resulting more directly from proliferation of leukaemic cells (lymphadenopathy, splenomegaly, hepatomegaly, bone pain, testicular enlargement and, in the case of T-ALL, respiratory difficulty resulting from thymic enlargement). Occasional patients present with abdominal masses resulting from massive renal infiltration.
In patients presenting with lymphoma rather than leukaemia, there may be thymic disease without involvement of the bone marrow and blood (T lymphoblastic lymphoma) or soft tissue involvement (T or B lymphoblastic lymphoma).
Haematological and pathological features
The peripheral blood usually shows anaemia, thrombocytopenia and leucocytosis, the latter as a result of the presence of leukaemic blast cells in the circulation (Figure 2.1). Less often there is anaemia and thrombocytopenia with few if any circulating blast cells.
Peripheral blood film from a patient with T-lineage ALL showing severe thrombocytopenia and two blast cells. Romanowsky stain, x 100 objective.
Some patients have reactive eosinophilia and occasionally eosinophils are very numerous. The blast cells are usually small to medium sized with a high nucleocytoplasmic ratio and sometimes nucleoli. Smaller blast cells can show some chromatin condensation. Cells are regular in shape in the majority of cases and much more pleomorphic in a minority. Cytoplasm is weakly to moderately basophilic; it may contain vacuoles and, less often, peroxidase-negative granules. In occasional patients there is a polar cytoplasmic projection, cells being described as 'hand-mirror cells'. Blast cells are negative for myeloperoxidase and chloroacetate esterase. They may be negative with Sudan black B or stain very weakly; when a counter-stain ...