Other tumors
Plexiform fibromyxoma

Topic Completed: 16 June 2020

Minor changes: 26 January 2021

Copyright: 2003-2021,, Inc.

PubMed Search: gastric plexiform fibromyxoma

Yujun Gan, M.D., Ph.D.
Xiuli Liu, M.D., Ph.D.
Page views in 2020: 2,910
Page views in 2021 to date: 1,079
Cite this page: Gan Y, Liu X. Plexiform fibromyxoma. website. Accessed April 16th, 2021.
Definition / general
Essential features
  • Benign mesenchymal neoplasm that predominantly arises in the gastric antrum and pyloric region
  • Multinodular and plexiform architecture with arborizing vasculature at low power
  • Cytologically bland spindle cells in myxoid or fibromyxoid stroma
  • Rare or no mitotic figures; low proliferation index in most cases
  • Metastases and recurrence following complete excision have not been described
  • Also known as plexiform angiomyxoid myofibroblastic tumor
ICD coding
  • ICD-O: 8811/0 - Plexiform fibromyxoma
  • ICD-11: 2E92.1 - Benign neoplasm of stomach
  • Recurrent MALAT1-GLI1 translocation or GLI1 upregulation have been identified in a subset of plexiform fibromyxomas (J Pathol 2016;239:335)
Clinical features
  • Symptoms include upper gastrointestinal bleeding, abdominal distension, abdominal pain, nausea, hematemesis, anemia, weight loss, obstruction
  • Some cases are incidental endoscopic finding in asymptomatic patients
Case reports
Clinical images

Contributed by Yujun Gan, M.D., Ph.D. and Xiuli Liu, M.D., Ph.D.

Large gastric antral mass

Large mural hypoechoic mass

FNA of the mass

Gross description
  • Presents most commonly as a solitary, circumscribed, multilobulated mass centered in the muscularis propria
  • Overlying mucosa may be smooth and unremarkable but sometimes is ulcerated
  • Tumor size varies from 1.5 cm up to 15 cm (Am J Surg Pathol 2009;33:1624)
Gross images

Contributed by Yujun Gan, M.D., Ph.D. and Xiuli Liu, M.D., Ph.D.

Antral mass

Myxoid and cystic degeneration

Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Yujun Gan, M.D., Ph.D. and Xiuli Liu, M.D., Ph.D.

Hypocellular and myxoid tumor

Bland spindle cell proliferation

Fibrillary stroma

Spindle and myxoid tumor

Smooth muscle actin immunoreactivity

Contributed by Raul S. Gonzalez, M.D.

Plexiform architecture

Bland myxoid tumor

Negative stains
Sample pathology report
  • Stomach, antrum, endoscopic submucosal dissection:
    • Plexiform fibromyoxoma, completely excised (see comment)
    • Comment: There is a bland spindle cell proliferation within myxoid stroma. Prominent vasculature transverses the lesion. No significant pleomorphism is noted. No mitotic figures or necrosis are noted. The tumor cells are positive for smooth muscle actin but negative for CD34, c-kit / CD117, desmin, S100 and DOG1. The overall histology and immunophenotype are most consistent with plexiform fibromyxoma. Metastases and recurrence following complete excision of plexiform fibromyxoma have not been reported.
Differential diagnosis
  • GIST:
  • Inflammatory fibroid polyp:
    • Primarily arises in the submucosa
    • Has more inflammation and often demonstrates a concentric growth of spindle cells around small blood vessels
    • In most cases, the spindle cells are CD34 positive
  • Neurofibroma:
    • Neurofibroma can demonstrate a plexiform growth pattern
    • Consists of multiple cell types including S100 positive schwann cells intermixed with CD34 positive spindled fibroblasts and EMA positive perineurial cells
  • Schwannoma:
    • Comprises diversely arranged tumor cells that often form a microtrabecular structure against a background of collagen
    • Characteristic histological features include intralesional lymphoplasmacytic inflammation and lymphoid cuff with infiltrative margin
    • Schwannoma cells are S100 and SOX10 positive
  • Inflammatory myofibroblastic tumor (IMT):
    • Often affects children or young adults
    • Most common locations are mesentery and omentum
    • IMT comprises spindled to stellate myofibroblastic cells with a lymphoplasmacytic background
    • About 50% of cases harbor rearrangements of anaplastic lymphoma kinase (ALK) gene and thus are positive for ALK by immunohistochemistry
  • Fibromatosis:
Board review style question #1

Which of the following is true about plexiform fibromyxoma?

  1. Complete resection of the lesion provides cure
  2. Metastases are common after complete resection
  3. Most plexiform fibromyxomas are malignant
  4. Plexiform fibromyxoma only occurs in the stomach
  5. Recurrent translocation of genes have not been reported
Board review style answer #1
A. Complete resection of the lesion provides cure

Reference: Plexiform fibromyxoma

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Board review style question #2
A 71 year old woman presented with vague upper abdominal pain. EGD examination reveals a 4.5 cm mural mass in the antrum. The patient underwent partial gastrectomy. Gross examination reveals a multilobular mural mass. The tumor shows a bland spindle cell proliferation in a variably myxoid stroma. The tumor cells are positive for smooth muscle actin but negative for CD34, CD117, desmin, ALK, S100 or DOG1. Which of the following is most likely the correct diagnosis?

  1. Gastrointestinal stromal tumor
  2. Inflammatory fibroid polyp
  3. Neurofibroma
  4. Plexiform fibromyxoma
  5. Schwannoma
Board review style answer #2
D. Plexiform fibromyxoma

Reference: Plexiform fibromyxoma

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