Meyron

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

Azathioprine

Group 1 — carcinogenic to humansMedications & MedicalbehavioralEvidence: sufficient_in_humans

Quick answer

Classified as Group 1 — carcinogenic to humans, based on sufficient evidence in humans. Prescription medication. Taken after organ transplant or for some autoimmune conditions to suppress the immune system.

Summary

An immunosuppressive medication used after organ transplant. Associated with non-Hodgkin lymphoma and skin cancer.

Detail

Azathioprine is Group 1 with sufficient evidence for non-Hodgkin lymphoma and squamous cell skin cancer. Used after organ transplant and for some autoimmune conditions. Transplant recipients as a group have increased risks of several cancers (the immunosuppression itself is the carcinogenic exposure). Questions about whether azathioprine is appropriate are clinical decisions between a patient and their care team.

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

global

global

Documented in these products

Organ transplant / immunosuppressants

Presence in a product category doesn't imply the product causes cancer. Click each to see the source and context.

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: Immunosuppression

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IARC

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

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Supporting sources

ACS

ACS — Known and Probable Human Carcinogens

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NTP

NTP — Report on Carcinogens (US National Toxicology Program)

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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.