Mutations in c-kit Gene Exons 9 and 13 in Gastrointestinal Stromal Tumors among Japanese

Gain-of-function mutation in c-kit proto-oncogene exon 11 has been described in about 20-50% of gastrointestinal stroma tumor (GIST). Recently, additional mutational hot-spots in exon 9 and exon 13 of the c-kit gene have been reported in GISTs without mutations of exon 11, but a subsequent report in a Western population indicated that only a small portion of GISTs (eight of 200 GISTs, 4%) showed mutations in these regions. In this study, we evaluated mutations in exon 9 and exon 13 of the c-kit gene by both polymerase chain reaction-single strand conformation polymorphism analysis and direct sequencing in 48 GISTs in a Japanese population, for which the clinicopatho-logical and immunohistochemical features and mutations in exon 11 had previously been reported. C-kit gene mutation in exon 9, representing insertion of GCC TAT, was identified in only 4 of 48 GISTs (8%), and none of the GISTs had mutations in exon 13. All four GISTs with mutation in exon 9 were high-risk, and the patients died of multiple tumor metastasis. Mutations in exon 9 and exon 13 of the c-kit gene were also rare events in Japanese GISTs and were related to a poor prognosis. These results in Japanese are consistent with those in Western populations, although a preferential occurrence of GISTs with exon 9 mutation in the small intestine, which was suggested in a previous report, was not observed.