Methotrexate‐associated lymphoproliferative disorder: A rare pancreatic tumor diagnosed via endoscopic ultrasound‐guided fine‐needle biopsy

Abstract A 73‐year‐old woman with a history of rheumatoid arthritis treated with methotrexate (MTX) for the last 10 years was referred to our hospital for a pancreatic tumor examination. Contrast‐enhanced abdominal computed tomography revealed a 20‐mm‐diameter hypovascular tumor in the pancreatic tail. A hypoechoic mass with heterogeneous internal echo was found on an endoscopic ultrasound (EUS). An EUS‐guided fine‐needle biopsy (EUS‐FNB) was performed with a 22‐gauge Franseen‐tip needle. Histologic examination of EUS‐FNB specimens from the pancreatic tumor revealed the proliferation of atypical spindle cells. Immunohistochemical staining for CD20 and Ki‐67 was positive in the atypical cells. Immunohistochemical staining for CD3 was partially positive in the atypical cells. Epstein–Barr virus‐encoded RNA in situ hybridization showed positive staining. MTX‐related lymphoproliferative disorder (MTX‐LPD) with Epstein‐Barr virus infection was diagnosed. MTX treatment was immediately discontinued, and treatment was initiated by a hematologist. However, her condition rapidly deteriorated, and she died of multiple organ failure 4 weeks after diagnosis. MTX‐LPD can complicate gastrointestinal lesions. However, most lesions are localized in the stomach and rarely complicate pancreatic lesions. MTX‐LPD is classified as an “iatrogenic” LPD. Therefore, immediate action, such as MTX discontinuation, is necessary. In conclusion, endoscopists should be aware that MTX‐LPD lesions can occur in the pancreas and gastrointestinal tract. Moreover, EUS‐FNB can be useful in the diagnosis of this rare pancreatic tumor.