[756] Plexiform Fibromyxoma of the Gastric Antrum: Clinicopathologic and Molecular Characterization of 5 Cases

Monika Tripathi, Hector Li Chang, Dimitrios Divaris, Ron Pace, Eva Szentgyorgyi, Andrea Grin, Brendan Dickson, Aaron Pollett, Catherine Streutker, Robert Riddell, Richard Kirsch. St. Michael's Hospital, Toronto, ON, Canada; Mount Sinai Hospital, Toronto, ON, Canada; Grand River Hospital, Toronto, ON, Canada; Toronto General Hospital, University Health Network, Toronto, ON, Canada

Background: Plexiform fibromyxoma is a recently described distinctive, mesenchymal neoplasm of the gastric antrum, which may be confused with a myxoid GIST, neurofibroma or inflammatory fibroid polyp. To date less than 20 cases have been reported. Limited follow-up data suggests that this tumor is benign. We report five additional cases with detailed clinicopathologic, histomorphological & molecular characterization.
Design: Five cases of plexiform fibromyxoma were retrieved from the consult files of 3 major academic centers in Toronto. Resection specimens were available on all cases. Clinicopathologic, histologic, immunohistochemical and molecular characteristics of these tumors were documented.
Results: Patients included three females & two males with an age range of 39 to 83 years (median age: 49). Presenting symptoms included epigastric discomfort & pain (n=4) and massive upper GI hemorrhage (n=1). All tumors involved the gastric antrum and one case also involved the first part of the duodenum. One case was associated with an incidental small intestinal GIST. Histologically, all five cases demonstrated a distinctive multinodular plexiform growth pattern which dissected through the muscularis propria. The tumors were composed of spindled to oval cells in a variably myxoid to collagenised stroma. A delicate arborizing vascular network was seen in 4 cases. Distinctive pseudolacunar spaces surrounded by a delicate fibrous meshwork were identified in 3 cases. Immunohistochemically all five cases were strongly positive for smooth muscle actin but negative for desmin, CD117 and DOG-1 and one showed patchy CD10 positivity. Of the 4 cases tested for KIT and PDGFRA mutations, all showed wild-type DNA sequences.
Conclusions: We describe a series of five plexiform fibromyxomas with similar clinical, morphologic, immunohistochemical and molecular features to the limited number previously reported. Awareness of its distinctive topographic, morphologic and immunohistochemical features should readily facilitate its distinction from potential mimics including myxoid GIST, inflammatory fibroid polyp and neurofibroma.
Category: Gastrointestinal

Wednesday, March 6, 2013 1:00 PM

Poster Session VI # 83, Wednesday Afternoon


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