Lack of c-kit exon 11 activating mutations in c-KIT/CD117-positive SCLC tumour specimens

Previous studies have shown that STI571, a selective tyrosine kinase inhibitor of c-KIT, is highly effective in c-KIT/CD117-positive gastrointestinal stromal tumours (GIST), especially those that have activating mutations in the c-kit exon 11 that encodes the juxtamembrane (JM) domain of the c-KIT oncoprotein. We examined the prevalence of activating exon 11 c-kit mutations in 26 small-cell lung cancer (SCLC) cases in order to explore whether this disease is also a potential target for treatment with STI571. Expression of c-KIT, estimated by immunohistochemistry, was demonstrated in 14 out of 22 SCLC samples (64%); nine samples showed moderate to strong staining (41%), five samples were weakly positive (23%), whereas eight samples (36%) were negative for CD117. Next, we examined the mutational status of exon 11 of the c-kit gene, by single-stranded conformational polymorphism (SSCP) and sequencing in all of the cKIT/CD117-positive tumours. However, no activating mutations in the c-kit exon 11 were found by either technique. Apparently, c-KIT oncoprotein expression in SCLC was not correlated with activating mutations in c-kit exon 11. In analogy to GISTs, our results could imply that SCLC patients would not benefit from treatment with STI571.