['Small cell lung cancer (SCLC) relapses rapidly after the initial response to chemotherapy and shows drug-resistance. This study was to investigate the efficacy and safety of cellular immunotherapy (CIT) with autologous natural killer (NK), γδT, and cytokine-induced killer (CIK) cells as maintenance therapy for SCLC patients.', 'A pilot prospective cohort study was conducted with SCLC patients who had responded to initial chemotherapy. Patients elected to receive either CIT as maintenance therapy (study group), or to be followed-up without further treatment (control group). Progression-free survival (PFS), overall survival (OS), and adverse effects were investigated.', 'We recruited 58 patients (29 in each group). The patient characteristics of the 2 groups were well balanced. PFS was not significantly different between the groups, but OS was significantly longer in the study group than the control (20 vs. 11.5 months, P\u2009=\u20090.005; hazard ratio [HR], 0.434, 95 % confidence interval [CI], 0.236-0.797, P\u2009=\u20090.007). Among patients with limited-stage disease, there was no difference in PFS between the groups, but OS was longer in the study group compared to the control (26.5 vs. 11.8 months, P\u2009=\u20090.033; HR, 0.405, 95 % CI, 0.169-0.972, P\u2009=\u20090.043). Among patients with extensive-stage disease, both PFS and OS were longer in the study group than the control (5 vs. 2.7 months, P\u2009=\u20090.037; HR, 0.403, 95 % CI, 0.162-1.003, P\u2009=\u20090.051, and 14.5 vs. 9 months, P\u2009=\u20090.038; HR, 0.403, 95 % CI, 0.165-0.987, P\u2009=\u20090.047, respectively). No significant adverse reactions occurred in patients undergoing CIT.'] Does cellular immunotherapy as maintenance therapy prolong the survival of the patients with small cell lung cancer?