March 2019 Case

Mary Wong, MD, MBA (Resident), Bonnie Balzer MD, PhD (Faculty)

The patient is a 60 year old male who was found to have a stomach mass along the lesser curvature of the stomach at an outside facility. He presented to Cedars-Sinai Medical Center for surgical management.

Plexiform fibromyxoma

Plexiform fibromyxoma is a very rare, benign mesenchymal neoplasm. It has also been reported in literature as plexiform angiomyxoid myofibroblastic tumor as well as myxoma. The age ranges from ranging from 7 to 75 years (mean age: 43), and the ratio of male-to-female is 1:1. The tumor predominantly involves the wall of the gastric antrum and may extend to the duodenum. Patients often clinically present with anemia or hematemesis, but larger tumors may cause gastric outlet obstruction.

Grossly, the tumor is often lobulated and unencapsulated with size ranging from 1.9 cm to 15 cm (mean size: 6.3 cm). Histologically, the tumor may be multinodular and has a plexiform architecture with prominent arborizing capillary network. It is composed of an abundant hypocellular fibromyxoid or collagenous matrix and has uniform small spindle cells with eosinophilic cytoplasm and inconspicuous nucleoli.

The differential diagnosis includes gastrointestinal stromal tumor (GIST), particularly the myxoid subtype, and plexiform neurofibroma. Generally, myxoid GISTs lack the plexiform architecture and have epithelioid cells in the lesion. These GISTs are positive for DOG1, KIT and CD34 immunostains. Plexiform neurofibromas generally have a more cellular myxoid stroma, are S100 positive, and occur in patients with neurofibromatosis type 1. In contrast, plexiform fibromyxomas are negative for DOG1, KIT, CD34 and S100.

Treatment is surgical resection. Recurrences or metastases have not been reported in literature.

1. Hornick, Jason L., MD, PhD. Practical Soft Tissue Pathology. Philadephia, PA: Saunders, an imprint of Elsevier Inc.; 2013.
2. Miettinen, Markku, MD, Maklouf, Hala R., MD, Sobin, Leslie H., MD, Lasota, Jerzy, MD. Plexiform Fibromyxoma: A Distinctive Benign Gastric Antral Neoplasm Not to be Confused With a Myxoid GIST. Am J Surg Pathol. 2009 Nov;33(11):1624-32
3. Odze, Robert D., MD, FRCP(C), Goldblum, John R., MD. Surgical Pathology of the GI Tract, Liver, Biliary Tract and Pancreas, 3rd edition. Philadephia, PA: Saunders, an imprint of Elsevier Inc.; 2015.