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Leukaemic Peripheral T-cell Lymphomas

Large Granular Lymphocytosis

Diagnosis and Assessment

• In almost all cases the lymphocytosis is due to an expanded population of cytotoxic T-cells rather than NK cells.
• The cells express CD3/TCRab and CD8 and varying combinations of CD16, CD56, CD57 and CD11b.
• Cases that are CD16⁺CD56^- are almost always monoclonal; most of the remainder are polyclonal.

Outcome and Treatment

• The main clinical problem is neutropenia; this may require growth factor support in a few patients
• Very few patients develop progressive disease and require chemotherapy
• Monoclonality in this context does not imply malignancy and has no special prognostic significance.

T-cell Prolymphocytic Leukaemia

Clinical Presentation

• Very rare with incidence <1 per million per year
• Presents with:
  • peripheral lymphocytosis; often very high and rising
  • lymphadenopathy
  • splenomegaly

Diagnosis

• Medium sized lymphocytes with round nucleus and prominent nucleoli in most cases. A rarer small cell variant is also seen.
• Immunophenotype:
  • CD3/TCRab, CD2 and CD4 with variable expression of T-cell activation markers
  • In a few cases a proportion of CD4/CD8 co-expressing cells are present with nuclear Tdt expression, suggesting that T-PLL arises from immediate post-thymocyte T-cells

Outcome and Treatment

• In most cases this is a highly aggressive malignancy although a few patients have a more indolent clinical course. This group is difficult to identify at presentation.
• The outcome with conventional treatment is poor.
• Anti-CD52 (CAMPATH 1H) may lead to rapid reduction in disease bulk.

Sezary Syndrome

Clinical Presentation

• The diagnosis of Sezary syndrome requires:
  • Peripheral T-cell leukaemia
  • Generalised skin infiltration
• Sezary syndrome may occur as an acute presentation or at the end stage of cutaneous T-cell lymphoma of mycosis fungoides type.
• Some patients may have a similar leukaemia but without skin infiltration.

Diagnosis

• Peripheral blood lymphocytosis and bone marrow involvement by small to intermediate sized T-cells with highly convoluted nuclei (?Sezary cells?)
• Immunophenotype:
  • CD3/TCRab, CD4, CD45RO, variable expression of other pan-T-cell antigens
• Skin biopsy shows dermal and epidermal infiltration.

Outcome and Treatment

• The outcome of Sezary syndrome arising de novo or in the context of long-standing mycosis fungoides is very poor
• Patients may be treated with combination chemotherapy but there is little evidence that this is effective.

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