Methotrexate-associated Lymphoproliferative Disorder Showing Colon and Liver Lesions Difficult to Distinguish from Colon Cancer with Liver Metastases.

An 82-year-old man presented with weight loss was being treated with methotrexate (MTX) for rheumatoid arthritis. Computed tomography revealed sigmoid colonic wall thickening and multiple liver masses. Although we initially considered sigmoid colon cancer with liver metastases, the patient was diagnosed with MTX-associated lymphoproliferative disorder (MTX-LPD) based on histopathological findings and clinical course. All the lesions improved after MTX discontinuation. MTX-LPD rarely affects the gastrointestinal tract, particularly the colon. However, our case suggests that MTX-LPDs should be considered when gastrointestinal lesions are observed in patients receiving MTX.