# HTLV-1 (human T-lymphotropic virus type 1)

Source: https://onco.cc/terms/lymphoma-htlv-1/  
OnCo record `lymphoma-htlv-1` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A virus that infects T cells, is passed mainly through breastfeeding and sexual contact, and causes a lymphoma decades later in a small minority of the people it infects. It is common in south-western Japan, the Caribbean, west and central Africa, parts of South America, Romania and Iran, and uncommon elsewhere.

## Summary

HTLV-1 was the first human retrovirus shown to cause a cancer. It infects CD4-positive T cells and integrates into their DNA, where its proteins Tax and HBZ drive proliferation and block the repair of damage. Most infections are acquired in infancy through breast milk; sexual transmission, transfusion of cellular blood products and shared needles account for the rest.

The great majority of people infected never develop a lymphoma, and infection is lifelong. The two diseases it causes are adult T-cell leukaemia/lymphoma, after a latency usually measured in decades, and a progressive neurological disease, HTLV-1-associated myelopathy or tropical spastic paraparesis. Infection also suppresses cell-mediated immunity, which is why strongyloides hyperinfection and opportunistic infection are common complications.

Where it matters clinically: HTLV-1 serology belongs in the work-up of any T-cell lymphoma in a person who comes from, or whose parents come from, an endemic region, because adult T-cell leukaemia/lymphoma is treated differently from every other T-cell lymphoma and is easy to mistake for peripheral T-cell lymphoma not otherwise specified. A systematic review of HTLV-1 among immigrants and refugees worldwide found a pooled prevalence of 1.28 per cent, highest among people from the Western Pacific region at 7.27 per cent, which is the practical argument for testing rather than assuming.

There is no vaccine and no treatment that clears the virus. Prevention rests on antenatal screening and avoidance of breastfeeding where that is safe, screening of blood donations, and barrier contraception.

## Fields

- Kind: Term
- Last checked: 2026-09-29
- Also known as: HTLV-1; HTLV-I; human T-cell lymphotropic virus type 1; human T-cell leukaemia virus type 1
- Tags: heme; lymphoma

## Sources

- WHO Classification of Haematolymphoid Tumours, 5th edition: lymphoid neoplasms (Alaggio, Leukemia 2022): https://doi.org/10.1038/s41375-022-01620-2
- The global prevalence of HTLV-1 and HTLV-2 infections among immigrants and refugees, systematic review and meta-analysis (Viruses 2024): https://doi.org/10.3390/v16101526

## Connected records

- pathways: [Oncogenic viruses](https://onco.cc/pathways/oncogenic-viruses/)
- terms: [Epstein-Barr virus (EBV) in cancer](https://onco.cc/terms/ebv-term/), [Lymphoma (tissue type)](https://onco.cc/terms/lymphoma-type/)
- cancers: [Adult T-cell leukaemia/lymphoma](https://onco.cc/cancers/adult-t-cell-leukaemia-lymphoma/), [Non-Hodgkin lymphoma (all types)](https://onco.cc/cancers/non-hodgkin-lymphoma/), [Peripheral T-cell lymphomas (including cutaneous T-cell lymphoma)](https://onco.cc/cancers/peripheral-t-cell-lymphoma/)

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