br Material and methods br Results br Discussion

Material and methods
Results
Discussion ES-SCLC is a disease with poor prognosis. Treatment outcome has not improved significantly during the last decades despite great efforts have been made. Maintenance therapy has been tried in several clinical trials with the aim to prevent the onset of recurrence and prolong survival. However, maintenance and/or consolidation using chemotherapy, cytokines and other biological agents failed to improve ES-SCLC outcomes [5]. Molecularly targeted drugs have been used as maintenance therapy in ES-SCLC in recent years, but most of them did not improve the OS of ES-SCLC patients, such as sorafenib, vandetanib, and imatinib [26–28]. Therefore, new therapeutic strategies are urgently needed to improve the outcome of this disease. Immune escape in SCLC patients is closely associated with the recurrence of the disease, and may contribute to poor patient survival [6,7,12–14]. Cancer SQ 22536 employ multiple mechanisms to evade an immune response [29–31], and thus CIT with only one type of immune cells is unlikely to achieve an optimal anticancer effect. In our previous study, CIT as maintenance therapy with the combination of NK, γδT and CIK cells has exhibited a synergistic anticancer effect and improved the outcome of SCLC patients, especially in ES-SCLC patients. The present study, with more patients enrolled and longer follow-up time, further confirmed the efficacy and safety of combined CIT as maintenance therapy for ES-SCLC patients. Thus, CIT may be a novel treatment for ES-SCLC patients who respond to first-line therapy, and can provide a novel strategy for the devastating disease. ES-SCLC is a highly malignant tumor associated with short survival and limited chemotherapy regimens, and hence there are fewer confounding factors for OS. In our study, OS was significantly longer after CIT in ES-SCLC patients. There are several possible reasons for the prolonged survival observed. Cancer stem cells (CSCs) have been reported to be responsible for cancer progression, metastasis, and the development of drug resistance [32,33]. They have also been shown to be susceptible to immunocyte-mediated toxicity, suggesting that CIT may be useful in eliminating minimal residual disease and thus reduce cancer recurrence [34–36]. Prolonged PFS and lower risk of recurrence (HR = 0.489) might be responsible for longer OS of ES-SCLC patients in the CIT group. But one study exploring the relationship between PFS and OS in SCLC patients found no significant relationship between them [37], suggesting that OS might be affected by other factors, such as second or third-line therapy. It has been reported that patients who received cancer vaccines responded better to subsequent chemotherapy than those who did not, suggesting that immunotherapy might sensitize cancer cells to cytotoxic drugs [38,39]. Indeed, patients with CIT tended to have higher CBR than the control in our study, although the difference was not significant, indicating that CIT might enhance the sensitivity of recurrent SCLC to second-line chemotherapy. It is noteworthy that only half of the patients in the control group received second-line chemotherapy, but most of the patients in the CIT group received second-line chemotherapy. The main reason why half of the patients in the control group didn\'t receive second-line chemotherapy was the low performance status. Only a very small number of patients didn\'t receive second-line chemotherapy because they refused further treatment. Therefore, CIT might improve the quality of life of cancer patients, so that more patients have the opportunity to receive second-line chemotherapy after CIT maintenance therapy. This might be another reason that CIT could prolong OS. The underlying mechanism needs to be further explored. Potential factors influencing the outcome of CIT were also evaluated in this study. Using a multivariate analysis, we found that sex, age, smoking history, ECOG performance status, chemotherapy course, radiotherapy and response to induction chemotherapy were not related to the efficacy of treatment. Patients receiving longer CIT course had longer PFS and OS. Both PFS and OS in patients who received more than 3 cycles of CIT was significantly longer than that of patients who received less than 3 cycles of CIT. OS was consistent with our previous report. In our previous study, PFS tended to be longer in patients who received more than 3 CIT cycles, but the different was not statistically significant. The difference between the two studies may be due to the different sample size and follow-up time. Besides, some patients with early stage SCLC were included in the previous study. One study demonstrated that NSCLC patients who received more than 7 cycles of CIK cell treatment had a significantly better prognosis than those who received fewer cycles [40]. Taken together, our findings and those of a previous report [40] suggest that a longer CIT course improved patient outcome. However, the optimal number of treatment cycle and the length of treatment course are yet to be determined. Even though the characteristics of the patients in these subgroups were well balanced, some patients stopped CIT treatment in the short course group because of disease progression. Therefore, the shorter PFS and OS might be affected not only by fewer CIT cycles, but also by other factors, such as the worse disease status in this subgroup of patients.