Identification of c-kit gene mutations in primary adenoid cystic carcinoma of the salivary gland

Abstract

The CD117 (KIT) protein is overexpressed in many human neoplasms including adenoid cystic carcinoma of salivary glands. To evaluate the function of c-kit-activating mutations in adenoid cystic carcinoma of the salivary gland, we studied 14 cases (13 primary, 1 cervical lymph node metastasis) from our institution. KIT protein expression was evaluated by immunohistochemistry using formalin-fixed paraffin-embedded tissue. Mutational analyses of c-kit extracellular (exon 9), juxtamembrane (exon 11) and tyrosine kinase domains (exons 13 and 17) were performed by polymerase chain reaction, clonal selection and DNA sequencing. All 14 cases demonstrated strong KIT expression by immunohistochemistry. Molecular analysis was successful in 8 of 14 cases, and c-kit missense point mutations were detected in seven of eight cases (88%) including seven in exon 11, two in exon 9, two in exon 13 and two in exon 17. Eight silent point mutations were detected in five cases. Two cases contained missense mutations in more than one exon. Different mutations were found in the primary tumor and the cervical lymph node metastasis of one patient. Point mutations in domains similar to those described in gastrointestinal stromal tumors were detected, including Pro551Leu and Lys558Glu (5' end of exon 11), Leu576Phe (3' end of exon 11), Val643Ala (exon 13) and Asn822Ser (exon 17). Additional novel point mutations in exons 9, 11, 13 and 17 were also identified. This study is the first to report c-kit gene mutations in primary adenoid cystic carcinoma of the salivary gland. Identification of such potential gain-of-function mutations in exon 11, and less frequently in exons 9, 13 and 17, suggests that KIT may be involved in the pathogenesis of adenoid cystic carcinoma of salivary glands. Our study raises a prospect of correlation of c-kit mutation and a potential treatment of adenoid cystic carcinoma with tyrosine kinase inhibitor (imatinib).

Figure 1

KIT immunohistochemical expression in primary adenoid cystic carcinoma of the salivary gland: (a) low-grade adenoid cystic carcinoma of the salivary gland with predominant cribriform/tubular pattern and (c) high-grade adenoid cystic carcinoma of the salivary gland with greater than 30% solid pattern with strong c-kit immunoreactivity in tumor cells (b, d). (a, b) Original magnification ×100; (c, d) magnification ×200.

Figure 2

KIT exon 11 mutational analyses in case of adenoid cystic carcinoma of the salivary gland. Multiple point mutations in exon 11 were detected in this case including Leu576Phe, similar to that described in gastrointestinal stromal tumors, novel mutations Pro551Leu and His580Tyr and a silent mutation in codon 578.

Figure 3

Adenoid cystic carcinoma of the salivary gland with KIT exon 13 point mutation Val643Ala, similar to a variant mutation found in gastrointestinal stromal tumors. The chromatogram tracing on the left depicts a wild-type sequence of KIT exon 13, codons 642–644. On the right is a case of adenoid cystic carcinoma of the salivary gland with a point mutation 1949T>C in codon 643, resulting in substitution of Valine for Alanine.

Figure 4

Adenoid cystic carcinoma of the salivary gland with KIT exon 17 point mutation Asn822Ser in hotspot region of codon 822. The wild-type KIT exon 17 sequence depicting codons 821–823 is illustrated on the left. On the right is a case of adenoid cystic carcinoma of the salivary gland with 2486A>G mutation, resulting in substitution of Asparagine for Serine in the frequently mutated c-kit region of codon 822.