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18 June 2014 - Case of the Week #316

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Thanks to Dr. Elaine Alt, Quest Diagnostics, New Jersey (USA), for contributing this case and discussion. To contribute a Case of the Week, follow the guidelines on our Case of the Week page.



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Case of the Week #316

Clinical History:
A 79 year old woman presented with a small gastric antral polyp.

Micro images:


What is your diagnosis?































Diagnosis:
Gastric plexiform fibromyxoma

Discussion:
Immunostains were obtained:

SMA

CD34

CD117

Desmin

Ki-67

S100



The biopsy shows a mucosa and submucosal multinodular proliferation of cytologically bland spindle cells with a myxoid background. Mitoses were not identified and Ki-67 demonstrates a very low proliferation index. The spindle cells are positive for SMA and negative for desmin, CD117, CD34 and polyclonal S100. Prominent arborizing capillaries are highlighted by the CD34 immunostain. These findings are consistent with gastric plexiform fibromyxoma, also known as a plexiform angiomyxoid myofibroblastic tumor (Am J Surg Pathol 2007;31:724, Am J Surg Pathol 2009;33:1624).

The differential diagnosis includes several other predominantly spindle cell lesions. An inflammatory fibroid polyp is usually a single nodule showing more inflammation and often demonstrating a concentric growth of the spindle cells around small blood vessels. In most cases, the spindle cells are CD34 positive. A GIST is often CD117 and CD34 positive and is usually not multinodular and myxoid. Neurofibromas are S100 positive.

Gastric plexiform fibromyxoma is a benign tumor recently added to the WHO Classification of Tumours of the Digestive System (IARC, 2010). It is considered rare and specific to the stomach. Most are multinoduar masses involving the muscularis propria or submucosa of the antral / prepyloric region, showing microscopically a multinodular proliferation of myofibroblastic cells and arborizing capillaries in a myxoid stroma (World J Gastroenterol 2010;16:2835). They have been seen over a broad age range. Metastases and recurrence following complete excision have not been described.

Nat Pernick, M.D., President
and Shivani Thakore, Associate Medical Editor
PathologyOutlines.com, Inc.
30100 Telegraph Road, Suite 408
Bingham Farms, Michigan (USA) 48025
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Email: [email protected]
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