A case of gastric/duodenal diffuse large B cell lymphoma observed during the administration of tacrolimus/azathioprine for dermatomyositis.

The patient was diagnosed with amyopathic dermatomyositis complicated with interstitial pneumonia (IP) at age 35. She had been treated with prednisolone and maintained on tacrolimus (TAC) + azathioprine (AZA). Eight years later, she experienced epigastric pain, and esophagogastroduodenoscopy (EGD) led to a diagnosis of duodenal ulcer. The pain did not improve, so she visited our hospital, where she presented with malaise, anemia, and weight loss. An EGD revealed submucosal tumor-like protrusions in the anterior and posterior walls of the gastric antrum and punched-out ulcers with auricle-like marginal swelling on the inside of the protrusions. Irregular-shaped punched-out ulcers were also observed in the duodenal bulb. Lymphoma was suspected, and biopsy was performed. Histopathology showed diffuse large, atypical lymphocytes with enlarged nuclei, and immunohistochemical staining revealed CD20-positive cells. Diffuse large B cell lymphoma (DLBCL) was diagnosed, which was considered as lymphomas arising in immune deficiency/dysregulation. After discontinuing TAC + AZA for three months, the gastrointestinal symptoms improved, and on EGD, the duodenal lesions had disappeared, with only a shallow depression covered with regenerated epithelium remaining in the posterior wall of the gastric antrum. Seven months later, the patient underwent follow-up EGD, and the disappearance of lymphoma cells was confirmed histopathologically by biopsy. Repeated and detailed endoscopic examination should be considered in an immunosuppressed patient with treatment-resistant gastric or duodenal ulcers.