Gastrointestinal stromal tumours of the colon (GIST)

Gastrointestinal stromal tumour more commonly occurs in the stomach.

This paper studied 37 GIST of the colon:

CD117	76% (19/25)
CD34	59% (16/27)
CD117 and CD34	54% (13/24)
SMA	23% (6/26): all SMA-positive cases were also CD117 positive
Desmin	0/27
S-100	0/27

Differential diagnosis

Smooth muscle tumours	SMA and desmin positive. Most are CD34 and CD117 negative
Inflammatory myofibroblastic tumours	CD117 negative
Liposarcoma	CD117 negative
Schwannoma	S-100 positive. CD34 and CD117 negative.
Metastatic melanoma or the rare primary intestinal clear cell sarcoma	S-100 and HMB-45 positive. May be CD117 positive
malignant vascular tumours	Commonly CD34 and CD117 positive. Also CD 31 positive.

Prognosis

1 cm or less in diameter	benign (4 cases)
5 cm or less in diameter and five or fewer mitoses per 50 HPFs	good prognosis: 2 of 10 patients died
5 cm or larger with more than five mitoses per 50 HPFs	poor prognosis: 14 of 17 patients died

Reference

Miettinen, M. Sarlomo-Rikala, M. Sobin, L. H. Lasota, J. Gastrointestinal stromal tumors and leiomyosarcomas in the colon: a clinicopathologic, immunohistochemical, and molecular genetic study of 44 cases. Am J Surg Pathol 2000; 24:1339-1352.