Gastric Plexiform Fibromyxoma

Definition

Plexiform multinodular growth pattern
- 1-7 mm nodules
Myxoid or fibromyxoid stroma
- Alcian blue positive
  - PASd negative
- Prominent arborizing capillaries
- Some nodules may have dense collagenous stroma
Cytologically bland oval nuclei
- 0-4/50 hpf mitotic count
- Indistinct cell borders
  - May have clear cytoplas
Generally hypocellular
- May have areas or nodules of increased cellularity
  - More commonly seen in extramural involvement
All cases involve the muscularis propria
- Frequent extension into submucosa and mucosa
- 50% extend into adjacent soft tissue or duodenum
  - Pushing border without plexiform pattern in areas of extragastric involvement
  - May form subserosal nodules
All cases reported in gastric antrum
- May extend into duodenum
Ulceration, mucosal invasion and vascular invasion may be seen
- None has any clinical significance
Absent features
- Tumor cell necrosis and calcification
- Nuclear palisading and skeinoid fibers

Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342