Posterior nasopharyngeal carcinoma associated with a high antibody titer to Epstein-Barr virus occurred in a 45-year-old man who had been receiving methotrexate therapy for psoriasis. Although this single case report does not establish methotrexate as a carcinogen in a class with arsenic, the action of immunosuppressive drugs in the body and the increased possibility that some cancers are virus-induced should alert others to be watchful for similar cases.
Craig SR, Rosenberg EW. Methotrexate-Induced Carcinoma?. Arch Dermatol. 1971;103(5):505-506. doi:10.1001/archderm.1971.04000170039009