Plexiform angiomyxoid myofibroblastic tumor of the stomach

Abstract

Plexiform angiomyxoid myofibroblastic tumor of the stomach is a unique mesenchymal tumor that we first described in 2007. The tumor is very rare, and to date, only 18 cases confirmed by immunohistochemistry have been reported in the literature. The patients' ages ranged from 7 to 75 years (mean, 43 years), and the male-to-female ratio was approximately 1:1. Representative clinical symptoms are ulceration, associated upper gastrointestinal bleeding (hematemesis), and anemia. The tumors are located at the antrum in all cases, and grossly, the tumor is whitish to brownish or reddish, and forms a lobulated submucosal or transmural mass. Microscopically, the tumor is characterized by a plexiform growth pattern, the proliferation of cytologically bland spindle cells, and a myxoid stroma that is rich in small vessels and positive for Alcian blue stain. Immunohistochemically, the tumor cells are positive for alpha-smooth muscle actin and negative for KIT and CD34. Differential diagnoses include gastrointestinal stromal tumor and other mesenchymal tumors of the gastrointestinal tract. Some authors proposed that this tumor should be designated as "plexiform fibromyxoma", but this designation might cause confusion. The tumor is probably benign and thus far, neither recurrence nor metastasis has been reported.

Figure 1

Gross appearance of a case of plexiform angiomyxoid myofibroblastic tumor (PAMT). A: A reddish and lobulated tumor protrudes from the serosa; B: The cut section of the tumor. The tumor causes ulceration and perforation.

Figure 2

Histological appearance of PAMT. A: The tumor shows a multinodular plexiform growth pattern (HE stain, × 20); B: Spindle-shaped bland tumor cells are separated by an abundant intercellular myxoid matrix. The stroma is rich in small vessels (HE stain, × 100); C: Tumor cells possess oval nuclei and a slightly eosinophilic cytoplasm. The nucleoli are inconspicuous and the cell borders are indistinct (HE stain, × 200); D: The stroma is positive for Alcian blue stain (× 200); E: Stromal collagenization is occasionally observed (HE stain, × 200).

Figure 3

The results of immunohistochemical staining. A: The tumor cells are negative for KIT. The scattered KIT-positive cells are mast cells (× 200); B: The tumor cells are diffusely positive for smooth muscle actin (× 200).