KIT-negative GISTs

CD117-negative GISTs most commonly occur in the stomach, but may also be found in the omentum, mesentery, peritoneum or small bowel. Mutations of platelet-derived growth factor receptor alpha (PDGFRA, 18/25 cases¹) are more common than KIT mutations (4/25 cases¹); some cases show neither (3/25¹).

KIT-negative GISTs more commonly occur in males. They are histologically similar to CD117-positive cases, with a greater predominance of epithelioid tumours. There may be a greater frequency of omental and peritoneal tumours.

Immunohistochemistry

To date, commercially available antibodies against PDGFRA do not yield reproducible results.

	CD34	11/231
	SMA	10/231
	S-100	1/23 (focal)1
	Desmin	0/231
	Cytokeratin	0/231

Management

One patient with a KIT-negative GIST has responded to off-protocol treatment with imatinib.

References

¹Heinrich, M. C., C. L. Corless, et al. (2003). "PDGFRA activating mutations in gastrointestinal stromal tumors." Science 299(5607): 708-10.