Serum expression level of IL-6 at the diagnosis time contributes to the long-term prognosis of SCLC patients.

Cytokines are vital mediators involved in tumor immunity. We aimed to explore whether the expression levels of IL-1 beta, TNF-alpha and IL-6 have impacts on prognosis of SCLC patients. In this study, we concluded 707 non-operable SCLC patients at stage III or IV into this study and analyzed the relationships between interleukins and OS/PFS by cox regression analysis and Kaplan-Meier analysis (log-rank test). As a result, under current standard chemotherapy, SCLC patients with higher IL-6 expression level had a shortened OS compared with those with normal level (HR: 0.381, 95% CI: 0.177-0.822, p=0.014). Furthermore, IL-6 expression level contributed mostly to patients without a smoking history. Non-smoking patients with a high IL-6 level showed a 6 months shortened OS than those with normal IL-6 level (10.50 vs 16.90 months, p=0.003 by Log-Rank test in Kaplan-Meier analysis). IL-6 had no obvious impacts on first-line PFS in these SCLC patients. To conclude, IL-6 acts as an independent factor of long-term prognosis of SCLC patients under current therapy.