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 predominance1,2.

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

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