Long-term survival in small cell lung cancer patients is correlated with high interleukin-2 secretion at diagnosis

Purpose: We have previously reported significant impairment of IL-2 secretion in patients with small cell lung cancer (SCLC) at the time of diagnosis. Impairment of IL-2 secretion correlated with reduced survival in SCLC. This new prognostic factor was independent of other factors of prognostic relevance in SCLC. The prognostic value of IL-2 secretion was comparable to the most predominant prognostic factors for survival in SCLC identified so far. We now report long-term survival data from these patients. Methods: The significance of correlations between single parameters in the test groups was calculated by using linear regression analysis, the Wilcoxon rank sum test, and Fisher's exact test. Using the Kaplan-Meier method, the log-rank test and the Cox regression model, we analyzed the relation of IL-2 secretion in whole blood cell cultures from 52 patients with SCLC at the time of diagnosis to established prognostic factors relevant for survival in SCLC. Results: IL-2 secretion correlates with survival in SCLC. In addition, survival analysis according to tumor response and level of IL-2 secretion at the time of diagnosis demonstrates that long-term survival can only be observed after complete response to chemotherapy and high initial IL-2 secretion. Conclusions: IL-2 secretion at the time of diagnosis represents an independent prognostic factor for survival in SCLC. Moreover, long-term survival is only observed in patients with complete response upon chemotherapy that showed high IL-2 secretion at diagnosis. Therefore, IL-2 secretion may partially define long-term survival in this disease. These results have to be confirmed in a larger patient population.