T- and NK-cell leukaemias and extranodal lymphomas
- Lesion
T and NK cells can become cancers of the blood, skin or nose. A virus (HTLV-1 or EBV) or a mutation in STAT3 sits behind several of them.
What it is
This family groups mature T- and NK-cell neoplasms that live mainly outside lymph nodes. Adult T-cell leukaemia/lymphoma is caused by HTLV-1 and presents with skin lesions, lymphadenopathy and hypercalcaemia. Mycosis fungoides and Sézary syndrome are tumours of skin-homing CD4 T cells. Large granular lymphocytic leukaemia is an indolent clone of cytotoxic T or NK cells that causes neutropenia. Extranodal NK/T-cell lymphoma is an EBV-driven, destructive tumour typically of the nose.
Structure
- ATLL: atypical T cells with clover-leaf nuclei in blood, skin and nodes.
- Mycosis fungoides: band-like infiltrate in the upper dermis with atypical lymphocytes climbing into the epidermis (epidermotropism) and forming Pautrier microabscesses.
- LGL leukaemia: large lymphocytes with abundant pale cytoplasm and coarse azurophilic granules.
- NK/T lymphoma: infiltrates around and into vessel walls with extensive ischaemic necrosis of nasal tissue.
Step by step
- ATLL: HTLV-1 infects CD4 T cells; the viral Tax protein activates growth genes, and over decades a clone emerges.
- Mycosis fungoides: a skin-homing CD4 T-cell clone settles in the epidermis and slowly expands.
- LGL: activating STAT3 mutations give cytokine-independent survival of cytotoxic cells, which suppress granulopoiesis.
- NK/T lymphoma: an EBV-infected NK cell (one clonal episome) expands and invades vessels, causing necrosis.
Extranodal T- and NK-cell neoplasms
| Entity | Cause or driver | Main sites | Key clues | Behaviour |
|---|---|---|---|---|
| Adult T-cell leukaemia/lymphoma | HTLV-1 | Blood, skin, nodes, liver, spleen | Flower cells, hypercalcaemia | Aggressive |
| Mycosis fungoides | Clonal skin-homing CD4 T cells | Skin | Patches and plaques, Pautrier microabscesses | Indolent for years |
| Sézary syndrome | Leukaemic variant of the same cells | Skin (erythroderma), blood, nodes | Cerebriform cells in blood | More aggressive |
| Large granular lymphocytic leukaemia | STAT3 mutations | Blood, marrow, spleen | Neutropenia, rheumatoid arthritis | Mostly indolent |
| Extranodal NK/T-cell lymphoma, nasal type | EBV | Nose, upper aerodigestive tract | Destructive midline lesion, necrosis | Aggressive |
Markers
- CD4
- CD25 (ATLL)
- CD8 and CD57 (T-LGL)
- CD56 (NK)
- EBER (EBV)
Clinical notes
- ATLL may follow decades of silent HTLV-1 carriage; the same virus causes HTLV-1-associated myelopathy.
- Mycosis fungoides can mimic eczema or psoriasis for years before biopsy.
- Nasal NK/T lymphoma is part of the differential of a necrotizing midline lesion, with granulomatosis with polyangiitis and mucormycosis.
Test yourself
Think of the answer, then tap the question to see it.
What are Pautrier microabscesses?
Small clusters of neoplastic cerebriform T cells within the epidermis in mycosis fungoides.
Which electrolyte disturbance is typical of adult T-cell leukaemia/lymphoma?
Hypercalcaemia.
Which virus is present in every tumour cell of extranodal NK/T-cell lymphoma?
Epstein–Barr virus, as one clonal episome.
Elsewhere in DurgiPedia
Connections
Microorganisms2
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Mycosis Fungoides (Including Sézary Syndrome) Treatment (PDQ®)–Patient Version (National Cancer Institute (NCI), 2026); Non-Hodgkin Lymphoma Treatment (PDQ®)–Patient Version (National Cancer Institute (NCI), 2026).
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Representative model, for educational purposes only.