KIT and gastrointestinal stromal tumor: The 4 cases with undetectable primary KIT mutations include GISTs with exon 11 c.1708_1728del (NCCS-GIST-07), exon 11 c.1669_1674del (NCCS-GIST-08), exon 11 c.1654_1659del and exon 13 c.1961T>C (NCCS-GIST-09), and exon 9 c.1504_1509dup (NCCS-GIST-10).