[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [White cells, lymph nodes, spleen and thymus](https://durgical.com/en/general-pathology/areas/hematolymphoid/) › T- and NK-cell leukaemias and extranodal lymphomas

# 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.

Updated Nov 12, 2026

## Key points

- ATLL: CD4 T cells with multilobed 'flower' nuclei; HTLV-1 endemic in southern Japan, the Caribbean, West Africa and parts of Latin America including the Colombian Pacific.
- Mycosis fungoides: patch, plaque and tumour stages; cerebriform CD4 cells and Pautrier microabscesses in the epidermis.
- Sézary syndrome: generalized erythroderma, lymphadenopathy and circulating cerebriform cells.
- LGL leukaemia: STAT3 mutations, neutropenia, anaemia, association with rheumatoid arthritis (some Felty syndrome).
- Extranodal NK/T-cell lymphoma, nasal type: angiocentric, necrotizing, EBV in every tumour cell.

On this page

- The basics Key points
- What it is
- Structure
- Step by step
- Extranodal T- and NK-cell neoplasms
- Markers
- Memory aid
- Elsewhere in DurgiPedia

- Clinical Clinical notes

- Study Test yourself

- Connections Connections

## 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](https://durgical.com/en/conditions/mycosis-fungoides-and-sezary-syndrome/) | Clonal skin-homing CD4 T cells | Skin | Patches and plaques, Pautrier microabscesses | Indolent for years |
| [Sézary syndrome](https://durgical.com/en/conditions/mycosis-fungoides-and-sezary-syndrome/) | Leukaemic variant of the same cells | Skin (erythroderma), blood, nodes | Cerebriform cells in blood | More aggressive |
| [Large granular lymphocytic leukaemia](https://durgical.com/en/conditions/neutropenia-and-drug-induced-agranulocytosis/) | 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.

## Memory aid

HTLV-1 makes flowers and raises calcium; mycosis fungoides makes Pautrier nests; EBV eats the nose.

## 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.

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## Elsewhere in DurgiPedia

- [CD4⁺ helper T cell](https://durgical.com/en/immunology/cd4-helper-t-cell/)
- [CD8⁺ cytotoxic T cell](https://durgical.com/en/immunology/cd8-cytotoxic-t-cell/)

## Connections

## Related 5

- [Nodal T-cell lymphomas](https://durgical.com/en/general-pathology/nodal-t-cell-lymphomas/)
- [Necrotizing lesions of the nose and upper airway](https://durgical.com/en/general-pathology/necrotizing-lesions-of-the-nose-and-upper-airway/)
- [Gastrointestinal lymphoma](https://durgical.com/en/general-pathology/gastrointestinal-lymphoma/)
- [Oncogenic viruses and H. pylori: the table to know](https://durgical.com/en/general-pathology/oncogenic-viruses-and-h-pylori-the-table-to-know/)
- [Paraneoplastic syndromes: the table to know](https://durgical.com/en/general-pathology/paraneoplastic-syndromes-the-table-to-know/)

## Related conditions 7

- [Mycosis fungoides and Sézary syndrome (cutaneous T-cell lymphoma)](https://durgical.com/en/conditions/mycosis-fungoides-and-sezary-syndrome/)
- [HTLV-1-associated myelopathy / tropical spastic paraparesis](https://durgical.com/en/conditions/htlv-1-associated-myelopathy-tropical-spastic-paraparesis/)
- [Hypercalcaemia of malignancy](https://durgical.com/en/conditions/hypercalcaemia-of-malignancy/)
- [Neutropenia and drug-induced agranulocytosis](https://durgical.com/en/conditions/neutropenia-and-drug-induced-agranulocytosis/)
- [Rheumatoid arthritis](https://durgical.com/en/conditions/rheumatoid-arthritis/)
- [Pure red cell aplasia (incl. Diamond–Blackfan anaemia)](https://durgical.com/en/conditions/pure-red-cell-aplasia/)
- [Non-Hodgkin lymphoma](https://durgical.com/en/conditions/non-hodgkin-lymphoma/)

## Microorganisms 2

- [Human T-lymphotropic virus type 1](https://durgical.com/en/microbiology/human-t-lymphotropic-virus-type-1/)
- [Epstein–Barr virus](https://durgical.com/en/microbiology/epstein-barr-virus/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

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](https://www.cancer.gov/types/lymphoma/patient/mycosis-fungoides-treatment-pdq) (National Cancer Institute (NCI), 2026); [Non-Hodgkin Lymphoma Treatment (PDQ®)–Patient Version](https://www.cancer.gov/types/lymphoma/patient/adult-nhl-treatment-pdq) (National Cancer Institute (NCI), 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/t-and-nk-cell-leukaemias-and-extranodal-lymphomas/