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Expression and Mutational Status of c-kit in Small-Cell Lung Cancer

Purpose: The c-kit protein, also known as CD117, is a member of the type III receptor tyrosine kinase family. Kinase activity has been implicated in the pathophysiology of many tumors, including small-cell lung carcinoma (SCLC). Autocrine or paracrine activation of c-kit by its ligand has been postulated for lung cancer, but this receptor can also be activated by mutations of the c-kit gene. We examined c-kit expression and mutational status in SCLC to verify its putative expression and genetic alterations, as well as its eventual prognostic impact. Experimental Design: We studied 60 SCLC samples to determine the mutations of the coding region of the gene; the exons 9 and 11 were analyzed by PCR-single-strand conformational polymorphism and automated sequencing. Moreover, c-kit expression was evaluated in 55 samples by immunohistochemical method. Results: Expression of c-kit was demonstrated in about 40% of SCLC samples. Two mutations in exon 9 and three mutations in exon 11 were found. Kaplan-Meier analysis revealed no prognostic significance of c-kit expression for survival. Conclusions: In our series, the expression of c-kit and its mutational status failed to appear relevant or to have a significant impact on survival; this makes the therapeutic approach with an inhibitor of tyrosine kinase more difficult in SCLC until a sure demonstration of c-kit implication is obtained for this tumor.