Meyron

Reference summary — not medical advice or a personal risk estimate.

Human T-cell lymphotropic virus type 1 (HTLV-1)

Group 1 — carcinogenic to humansInfectionsbiologicalEvidence: sufficient_in_humans

Quick answer

Classified as Group 1 — carcinogenic to humans, based on sufficient evidence in humans. Infection. Spread through blood, sexual contact, and breastfeeding. Most common in Japan, the Caribbean, parts of Africa and South America.

Summary

A virus that causes an aggressive adult leukemia/lymphoma in a small fraction of carriers.

Detail

HTLV-1 is Group 1 with sufficient evidence for adult T-cell leukemia/lymphoma (ATLL). Spread via blood, sexual contact, and from mother to child via breastfeeding. Infection is more common in Japan, the Caribbean, Africa and South America; most carriers do not develop disease.

What's not established

This classification is based on sufficient evidence in humans that this factor can cause cancer. It does not establish a safe exposure threshold, your personal risk, or how this factor's risk compares in size to other Group 1 agents — hazard classifications are not ranked by magnitude.

Regional relevance

east_asiacaribbeansouth_americaafrica

regional

Evidence sources

Every claim on this page traces back to one of these. Click through to read the primary document yourself.

Primary sources

NCI

NCI — Risk Factors: Infectious Agents

View source →

IARC

IARC Monographs — Classifications by Cancer Site, Vols 1–140

View source →

Supporting sources

ECDC

ECDC — Communicable diseases and cancer risk (European Centre for Disease Prevention and Control)

View source →

ACS

ACS — Known and Probable Human Carcinogens

View source →

NTP

NTP — Report on Carcinogens (US National Toxicology Program)

View source →

Last reviewed: October 2026

Official reference list

A government list some readers use alongside the primary evidence. Meyron is not affiliated with it. A chemical being listed does not by itself describe a risk from any particular product.