Two Cases of Plexiform Angiomyxoid Myofibroblastic Tumor (PAMT) of Gastrointestinal (GI) Tract: One With 8-Year Follow-up, One in Distal Jejunum

• Published in: American journal of clinical pathology Vol. 152; no. Supplement_1; p. S56
• Main Authors: Arslan, Mustafa Erdem, Jennings, Timothy, Li, Hua, Lee, Edward, Nigam, Ankesh, Lee, Hwajeong
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 11-09-2019
• Subjects: Actin; Biopsy; CD34 antigen; Cell proliferation; Cytokeratin; Desmin; Duodenum; Gastrointestinal cancer; Gastrointestinal tract; Growth patterns; Hematuria; Jejunum; Mesenchyme; Neoplasia; Small intestine; Tumors
• ISSN: 0002-9173; 1943-7722
• DOI: 10.1093/ajcp/aqz113.047

Abstract
Objectives
PAMT is an exceedingly rare mesenchymal tumor of the gastric antrum that was first described in 2007. Although likely benign, long-term follow-up is limited due to its recent description and rarity. In small bowel, only four cases of PAMT have been reported, two in duodenum and two in proximal jejunum.
Methods
(A) A 16-year-old female presented with GI bleeding and gastric outlet obstruction. Imaging studies suggested a gastrointestinal stromal tumor (GIST) arising in duodenum. An open biopsy revealed a bland spindle cell neoplasm. Resection of the tumor was performed. (B) A 68-year-old male presented with an incidental mesenteric mass on imaging during hematuria workup. He underwent surgical resection of the mass to exclude a GIST.
Results
Case A was a 15.0-cm mass arising in gastric antrum, and case B was an 8.0-cm mass arising in antimesenteric side of distal jejunum. Both tumors showed multinodular plexiform growth pattern and foci of cystic changes, with a proliferation of bland spindle cells in a prominent myxoid matrix. Numerous vascular structures were noted without tumor necrosis, nuclear atypia, or mitotic activity. The lesional cells were positive for actin and negative for desmin. The lesional cells were negative for other markers including cytokeratin, CD34, CD117, DOG-1, S-100, and PDGFRA (case B). Both masses were based in the subserosa with focal extension to the muscularis propria in case A. Patient A was followed up for 8 years with no evidence of disease. Patient B was lost to follow-up.
Conclusion
While clinical presentation and imaging finding of PAMT overlap with GIST, PAMT appears to be more indolent. PAMT of distal jejunum has not been previously reported. Small bowel PAMT is much less common than gastric PAMT but can involve variable segments. PAMT may be underdiagnosed.