Does Methotrexate Increase Cancer Risk?
Methotrexate, a folate antagonist used for rheumatoid arthritis, psoriasis, and cancers, shows mixed cancer risk effects. Low-dose use for autoimmune conditions does not clearly raise overall cancer risk and may lower it for some types, but it elevates risks for others, especially skin cancers and lymphomas, based on long-term studies.[1][2]
What Do Large Studies Show on Overall Cancer Risk?
A Danish cohort of 13,000 rheumatoid arthritis patients on methotrexate found no increased overall cancer incidence compared to non-users; standardized incidence ratios (SIR) were 1.0 for solid tumors and slightly elevated at 1.3 for hematologic cancers.[1] A meta-analysis of 20 studies confirmed no broad elevation in malignancy risk with low-dose methotrexate (under 25 mg/week).[3] Higher doses for cancer treatment can cause secondary malignancies like leukemias years later, but this applies to oncology protocols, not autoimmune dosing.[4]
Why Is Skin Cancer Risk Higher?
Methotrexate use correlates with doubled risk of non-melanoma skin cancers (squamous cell and basal cell), with SIRs of 1.6-2.0 in multiple cohorts. A UK study of 10,000 patients linked cumulative exposure over 3 years to this rise, possibly due to folate depletion impairing DNA repair in sun-exposed skin.[2][5] Melanoma risk shows inconsistent elevation (SIR 1.5 in some data).[1] Patients often have confounding psoriasis or UV exposure histories.
Does It Raise Lymphoma Risk, and Is It Reversible?
Risk of lymphoma, particularly Epstein-Barr virus-linked subtypes, increases 2-4 fold in rheumatoid arthritis patients on methotrexate (SIR 2.4 overall).[1][6] Japanese data report 33 cases per 100,000 patient-years versus 5 in the general population.[7] Many cases regress after stopping the drug, termed "methotrexate-associated lymphoproliferative disorder" (MTX-LPD), supporting a causal role in immunosuppressed states.[6]
How Does It Affect Other Cancers?
No consistent links to lung, breast, colorectal, or prostate cancers; some studies show protective effects (e.g., SIR 0.7 for lung cancer).[1][3] Risk may compound with other immunosuppressants like anti-TNF agents.[2]
What Precautions Do Guidelines Recommend?
ACR guidelines advise skin cancer screening, sun protection, and annual dermatology checks for long-term users. Monitor for lymphoproliferative symptoms like unexplained fever or nodes; discontinue if lymphoma suspected.[8] EBV testing pre-treatment reduces MTX-LPD risk in high-prevalence areas.[7] No routine cancer screening beyond age-based norms, given neutral overall risk.
Sources:
[1] Ann Rheum Dis. 2013
[2] JAMA Dermatol. 2015
[3] Semin Arthritis Rheum. 2015
[4] J Clin Oncol. 2015
[5] Br J Dermatol. 2018
[6] Mod Pathol. 2017
[7] Cancer Sci. 2013
[8] ACR Methotrexate Monograph, 2019