[Extranodal NK/T-cell lymphoma, nasal type, developed in a patient with rheumatoid arthritis].

: It is well known that patients with rheumatoid arthritis (RA) have a higher risk of developing malignant lymphoma (ML) than the general population. Most of these lymphomas occur in patients receiving immunosuppressive (IS) agents such as methotrexate (MTX). Spontaneous regression of tumors is often observed after the discontinuation of IS drugs, especially in patients with Epstein-Barr virus-positive lymphoma. Here we encountered an RA patient who developed extranodal NK/T-cell lymphoma, nasal type during treatment of RA with MTX and etanercept. Despite the discontinuation of MTX and etanercept, the tumor did not show any regression. Complete response was achieved after treatment with concurrent chemoradiotherapy. ML of NK-cell origin is extremely rare, while the majority of ML cases associated with RA are of B-cell origin. This report describes extranodal NK/T-cell lymphoma, nasal type case associated with RA. Such cases should be accumulated to evaluate the mechanism of onset and clinical characteristics of NK/T-cell lymphoma associated with RA.