Gastrointestinal stromal tumour of the soft tissue

Definition

A stromal tumour equivalent to that found in the gastrointestinal tract, positive for CD117.

Epidemiology

Patients are adult, with a female predominance^1,2.

Clinical features

Extra-gastrointestinal stromal tumours may occur at a range of sites, including abdominal cavity, mesentery, omentum, retroperitoneum and pelvic cavity.

Macroscopic appearances

The tumours form lobulated firm masses¹. There may be cystic change¹.

Histopathology

The appearances are identical to those occurring in the gastrointestinal tract. The spindle cell types are somewhat more common than the epithelioid type¹.

Immunohistochemistry

	CD117	39/39 (33 strong and diffuse, 6 diffuse but weak: these 6 cases stained strongly for CD34)1, 12/12 (in each case, most cells stained, with accentuation of the cell borders)2, 13/143
	CD34	24/391, 12/242, 12/213
	NSE	8/172
	SMA	11/391, 6/222, 15/233
	Desmin	2/391, 1/222, 1/23 (one case showed focal positivity)3
	S-100	2/391, 1/222
	Chromogranin	0/132

The rate of SMA positivity may be higher than in gastric GISTS³.

Differential diagnosis

• Leiomyosarcoma

• Leiomyomatosis peritonealis disseminata: occurs in young women as multiple nodules without a dominant mass, but associated with uterine leiomyomata.

• Intra-abdominal desmoid: there is a prominent vascular pattern; there is negativity for CD117 and CD34. Desmin and SMA positivity, if present, are limited.

• dedifferentiated liposarcoma: may be positive for CD34 but are negative for CD117³

• Solitary fibrous tumour: positive for CD34 but negative for CD117

• nerve sheath tumour: positive for S-100

• inflammatory myofibroblastic tumour

• Epithelioid type: leiomyoblastoma

Prognosis

Metastases may occur to liver, lung and bone.

Cases may be classified as¹:

• high risk: mitoses >= 5/50 HPF and >= 10% Ki-67 index

• medium risk: (mitoses >= 5/50 HPF and <10% Ki-67 index) or (mitoses < 5/50 HPF and >=10% Ki-67 index)

• low risk: mitoses < 5/50 HPF and <10% Ki-67 index

Tumour size does not seem to be of prognostic significance at these anatomic sites¹.

Others have found a mitotic rate >2/50HPF and necrosis to be independent predictors of a poor prognosis².

References

¹Yamamoto, H., Y. Oda, et al. (2004). "c-kit and PDGFRA mutations in extragastrointestinal stromal tumor (gastrointestinal stromal tumor of the soft tissue)." Am J Surg Pathol 28(4): 479-88.

²Reith, J. D., J. R. Goldblum, et al. (2000). "Extragastrointestinal (soft tissue) stromal tumors: an analysis of 48 cases with emphasis on histologic predictors of outcome." Mod Pathol 13(5): 577-85.

³Miettinen, M., J. M. Monihan, et al. (1999). "Gastrointestinal stromal tumors/smooth muscle tumors (GISTs) primary in the omentum and mesentery: clinicopathologic and immunohistochemical study of 26 cases." Am J Surg Pathol 23(9): 1109-18.

This page last revised 22.4.2004.

©SMUHT/PW Bishop