Plexiform angiomyxoid myofibroblastic tumor of the stomach: report of two cases and review of the literature

Abstract

Plexiform angiomyxoid myofibroblastic tumor (PAMT) of the stomach is a recently recognized entity. Because of its rarity, only 22 cases have been reported in the English-language literature and most of these are single case reports. We report two cases of gastric PAMT. The tumor cells were bland and plexiform arranged in a myxoid stroma, which was positive for alcian blue. Immunohistochemically, the tumor cells were positive for smooth muscle actin, but negative for c-kit, CD34, desmin, S-100 protein, epithelial membrane antigen, neurofilament, and protein kinase C-theta. Mutation analyses for exon 9, 11, 13, and 17 of KIT genes and 12, 14, and 18 of the platelet-derived growth factor receptor alpha (PDGFRA) genes were performed and the tumors were wild-type for mutation.

Keywords: Angiomyxoid; Myofibroblasts; Plexiform; Prognosis; Review; Stomach.

Fig. 1

(A) Computed tomography scan demonstrates about a 2 cm-sized prominent enhancing lesion on the gastric body and greater curvature side. There is no enlargement of any lymph node at the peritoneum or retroperitoneum. (B) On endoscopy, a 3×2 cm-sized, flat lesion with mucosal ulceration is found at the mid body, posterior wall and greater curvature of the stomach (case 1).

Fig. 2

(A) The tumor demonstrates a multinodular plexiform growth pattern. (B) Spindle tumor cells on abundant myxoid stroma. (C) The abundant stroma is positive for alcian blue stain. (D) The tumor cells are negative for CD34 (case 1).

Fig. 3

(A) The tumor is composed of bland looking spindle cells, a myxoid stroma and rich small vessels. The spindle tumor cell is admixed with myxoid or fibromyxoid stroma without any cytologic atypia. Nuclei are oval to slightly elongated, and cytoplasms are faintly eosinophilic. (B) The stroma contains abundant variable shaped small vessels and is positive for alcian blue stain. (C) On immunohistochemical staining, the tumor cells are negative for S-100 protein, but positive (D) for smooth muscle actin (case 2).