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Other iatrogenic immunosuppressive‐associated lymphoproliferative disorders (OIIA‐LPDs) rarely occur in the central nervous system (CNS). Additionally, they almost always present as lymphoma and withdrawal by cessation of immunosuppressive treatment. We report a case of primary CNS OIIA‐LPD that presented as extraosseous plasmacytoma (EP) with a progressive clinical course in spite of immunosuppressive treatment cessation. A 78‐year‐old man with a history of rheumatoid arthritis (RA) presented with a month‐long headache. Magnetic resonance imaging showed mass lesions in the left temporal lobe, left middle fossa, and intradural cervical spine. The left temporal lesion was resected and diagnosed as EP histologically, and OIIA‐LPD presented as plasmacytoma integrally due to his history of immunosuppressive treatment using tacrolimus for RA. Despite immunosuppressive treatment cessation, OIIA‐LPD lesions did not regress but, on the contrary, showed a progressive clinical course. Considering his advanced age and renal dysfunction, postoperative treatment with radiation and moderate chemotherapy using prednisolone were administrated. Subsequently, the disease state stabilized, and the patient had a Karnofsky performance status score of 90 for 6 months; however, the tumor recurred with meningeal dissemination, and he died 8 months after treatment. Types of OIIA‐LPD onset as EP and its progressive clinical course resistant to cessation of immunosuppressive treatment are rare. Moreover, this OIIA‐LPD disease state worsened despite its radiosensitivity. We believe the progressive clinical course of this OIIA‐LPD case with its high cell proliferation is similar to Epstein–Barr virus negative plasmablastic lymphoma, which could lead to a poor outcome. [ABSTRACT FROM AUTHOR]