Anaplastic lymphoma kinase-positive large B-cell lymphoma presenting as a submucosal tumor-like lesion at the esophagogastric junction: a diagnostic pitfall.

Anaplastic lymphoma kinase (ALK)-positive large B-cell lymphoma (LBCL) is a rare, aggressive variant of diffuse LBCL with an immunoblastic/plasmablastic morphology, a plasmacytic immunophenotype with loss of conventional B-cell antigens, and granular cytoplasmic ALK expression. Involvement of the gastrointestinal tract has been documented only in the stomach, duodenum, and ileum. To the best of our knowledge, we report the first case presenting at the esophagogastric junction. A 71-year-old immunocompetent man with Parkinson's disease was referred for progressive anemia that had been detected incidentally, and was found to have a submucosal tumor-like lesion with surface ulceration at the esophagogastric junction, despite a normal serum lactate dehydrogenase level. An endoscopic biopsy revealed diffuse sheets of large immunoblastic and plasmablastic cells. The cells were positive for CD138, multiple myeloma oncogene 1 (MUM1), epithelial membrane antigen (EMA), c-Myc, and CD4; exhibited lambda light-chain restriction; displayed granular cytoplasmic ALK positivity; and weakly expressed CD79a and paired box 5 (PAX5) in Golgi pattern and diffuse patterns, respectively. They were negative for CD30, CD3, CD5, CD8, Epstein-Barr virus-encoded small RNA, human herpesvirus-8, and pan-cytokeratin. Break-apart fluorescence in situ hybridization confirmed ALK rearrangement. Positron emission tomography demonstrated Ann Arbor stage IV disease, with nodal region involvement on both sides of the diaphragm in addition to the gastric cardia. This case illustrates a multilayered clinical, morphological, and immunophenotypic diagnostic pitfall, which was nonetheless resolved through endoscopic biopsy alone. The diagnostic value of this report lies in the lessons for avoiding misdiagnosis rather than in the rarity of the anatomical site.