Primary Gastric Alveolar Rhabdomyosarcoma: A Potent Mimicker of Neuroendocrine Carcinoma.

Alveolar rhabdomyosarcoma (ARMS) is a malignant tumor with skeletal muscle differentiation that usually occurs in soft tissues of the extremities or trunk. To date, only a few cases of primary gastric ARMS have been reported. Herein, we describe a case of ARMS in a man in his 80s and present a literature review. A submucosal tumor-like lesion was detected endoscopically. Histologically, the tumor cells exhibited a poorly differentiated morphology with hyperchromatic nuclei. Neuroendocrine markers, such as synaptophysin and CD56, were positive, and neuroendocrine carcinoma (NEC) was considered a differential diagnosis. However, both myogenic markers and OLIG2, which reflect FAX3 or FAX7 fusion, were positive, leading to a diagnosis of ARMS. Primary gastric ARMS is an extremely rare condition. Better awareness of this entity and its similarity to NEC is necessary for appropriate diagnosis and treatment.