Expression of the tyrosine kinase c-kit is an independent prognostic factor in patients with small cell lung cancer

In a retrospective analysis of 203 patients with small cell lung cancer (SCLC), we examined the prognostic value of c-kit expression on survival. Expression of c-kit was examined immunohistochemically in formalin-fixed, paraffin-embedded tissue sections. c-kit was observed in 87.7% of SCLC tumors. Using the Kaplan-Meier model, we found that lack of c-kit expression was associated with significantly shorter survival time compared to the presence of c-kit expression (mean survival 151 ± 27 vs. 358 ± 49 days, p = 0.0084). Moreover, the proportion of c-kit⁺ cells within the tumor was also related to survival time. Patients with tumors in which >75% of cells stained positive for c-kit had a mean overall survival time of 424 (±72) compared to 295 (±67) days for patients with 25-75% c-kit⁺ tumor cells. Patients with tumors containing <25% c-kit⁺ cells had the worst survival, with 164 (±24) days (p = 0.0033). Further parameters associated with short survival times were low performance status, elevated levels of lactate dehydrogenase and higher stage according to the TNM classification. Multivariate analysis using the Cox regression model showed that the proportion of c-kit⁺ cells within the tumor specimen was one of 3 independent prognostic parameters (p = 0.004) for overall survival next to TNM classification (p = 0.001) and performance status (p < 0.001).