Presence of smooth muscle cell differentiation in plexiform angiomyxoid myofibroblastic tumor of the stomach: a case report.

Plexiform angiomyxoid myofibroblastic tumor (PAMT) is a recently described distinctive gastric mesenchymal entity with a peculiar plexiform pattern, bland spindle cells and a myxoid stroma rich in arborizing blood vessels. In this study, we report a new case of this rare gastric tumor with a subset of tumor cells derived from smooth muscle differentiation. A 32-year-old Chinese man was admitted with a gastric mass. He did not experience any discomfort, and gastroscopy showed an elevated mass in the anterior wall of the gastric antrum. Endoscopic ultrasound examination revealed a focal hypoechoic lesion protruding into the lumen. A partial gastrectomy was performed, and the patient made an uneventful recovery and remains well 3 years later. The tumor in this case depicted all the typical histopathologic and immunochemical features of gastric PAMT, except that a small subset of tumor cells was partially immunoreactive for desmin and H-caldesmon. Based on the findings of this case, we think that PAMT may contain tumor cells derived from smooth muscle differentiation, and therefore this tumor may be more than just purely myofibroblastic in nature.