Mutational analysis of EGFR and KIT in thymic epithelial tumor

Abstract

18049 Background: Thymic epithelial tumor has been reported to express the epidermal growth factor receptor (EGFR), and thymic carcinoma has recently been described to have overexpression of KIT. We investigated the prevalence of EGFR and KIT mutations in patients with thymoma and thymic carcinoma to explore the potential for a targeted therapy with tyrosine kinase inhibitors. Methods: Genomic DNA was isolated from 41 paraffin-embedded tumor samples including 24 thymoma and 17 thymic carcinoma. EGFR mutations in exons 18, 19 and 21, and KIT mutations in exons 9, 11, 13 and 17, were analyzed by PCR and direct sequencing. Protein expressions of EGFR and KIT were also evaluated by immunohistochemistry. Results: We detected the EGFR mutation in 2 of 20 thymoma, but none of thymic carcinoma had mutation. All of the detected EGFR mutations were missense mutations in exon 21 (L858R and G863D, respectively). Expression of EGFR was seen in 71% of thymoma and 53% of thymic carcinoma. On mutational analysis of KIT, only one thymic carcinoma displayed a missense mutation in exon 11 (L576P). Expression of KIT was observed in 88% of thymic carcinoma and 0% of thymoma. Conclusions: Our findings indicate that a small number of patients with thymic epithelial tumor exhibit somatic mutations of EGFR or KIT although expressions of EGFR or KIT are present frequently in thymic epithelial tumor. Further investigations are warranted to determine their susceptibility to tyrosine kinase inhibitors in the treatment of thymoma and thymic carcinoma with EGFR or KIT mutations. No significant financial relationships to disclose.