Predicted imatinib response and GIST characteristics based on the mutation of the primary tumor in the KIT or PDGFRA genes.

Mutation Frequency Response
to Imatinib *		 Histological
cell type		 Anatomical
Site
KIT gene 80-85% mostly spindle
(long tapered
shape)

 any site

exon 9

10%

~80%

small bowela

exon 11

60-70%

~93%

any

exon 13

1%

~100% b

any

exon 17

1%

~75%

any
PDGFRA gene 5-10% epithelioid
(round shape)
or mixed
(spindle and
epithelioid)

usually stomach
exon 12

1%

some b
exon 14

<1%

unknown
exon 18

6%

none
Wild Type adult GIST c
(no KIT or
PDGFRA mutation)		 10%

~66%
more with stable disease than with
partial response

any type any site
* reported as "clinical benefit" including response or stable disease based on combined data from 3 clinical trials: B2222, EORTC phase I-II, EORTC Phase III.
a Rarely gastric GIST can be exon 9. About a third of small intestinal GISTs are exon 9 mutant (remainder are exon 11).
b Few data available.

c Pediatric/adolescent GISTs are usually wild-type but differ from adult wild-type GISTs in terms of histology and drug responsiveness.