Plexiform angiomyxoid myofibroblastic tumour of the stomach

Definition

This new entity has been proposed on the basis of two published cases1. It comprises bland spindle cells with a myxoid matrix with numerous small blood vessels and growing in a plexiform pattern.

Epidemiology

The two patients in whom this tumour has been described were 50 and 68 years old respectively, both male.

Clinical features

One tumour presented with perforation, the other was an incidental finding.

Macroscopic appearances

The tumours were lobulated extending from submucosal to transmural.

Histopathology

There was a plexiform growth pattern. The spindle cells were bland with slightly eosinophilic cytoplasm and oval nuclei. Mitoses are absent. The cells were embedded in a myxoid matrix which was positive for Alcian Blue. There were numerous small vessels. There were mast cells but no conspicuous inflammatory infiltrate.

Immunohistochemistry

	Vimentin	2/21
	SMA	2/21
	Muscle actin	2/21
	CD117	0/21
	CD34	0/21
	Desmin	0/21
	S-100	0/21
	Neurofilament	0/21
	Cytokeratin	0/21
	b-catenin	0/21
	Caldesmon	a few cells positive1
	Ki-67	<1% of cells1

Ultrastructure

Some cells showed intracytoplasmic microfilaments with focal condensations, subplasmalemmal densities and pinocytotic vesicles.

Molecular studies

No c-kit or PDGFRA gene mutations were identified.

Differential diagnosis

GIST: are positive for CD34 and CD117, show c-kit or PDGFRA mutations
Leiomyoma: the cytoplasm is strongly eosinophilic
Leiomyosarcoma: the cytoplasm is strongly eosinophilic
Schwannoma: nuclei are serpentine and palisade, the cells are positive for S-100.
Desmoid fibromatosis: the cells form long fascicles with dense collagen deposition, most cases are positive for b-catenin.
Solitary fibrous tumour: may show myxoid change but there is alternation of hypocellular and hypercellular areas, deposition of keloid-like collagen and positivity for CD34.
Inflammatory fibroid polyp: is usually submucosal. The spindle cells are concentric around blood vessels, there is an infiltrate of eosinophils
Inflammatory myofibroblastic tumour: there is an infiltrate of lymphocytes and plasma cells.
Fibromyxoma: cells are purely fibroblastic.

References

1 Takahashi Y, Shimizu S, Ishida T, et al. Plexiform angiomyxoid myofibroblastic tumor of the stomach. Am J Surg Pathol 2007; 31:724-8

This page last revised 2.6.2007.