The use of dendritic cells (DCs) for cancer vaccination is effective in suppressing cancer progression. This is because the DCs play a crucial role in priming tumor-specific immunity efficiently as antigen-presenting cells. In this study, we analyzed the ability of DCs to elicit tumor-specific immunity and clinical effects of DC vaccine immunotherapy targeting MUC1 tumor antigens. DCs from 14 patients with advanced or metastatic breast or lung cancer (9 positive for MUC1 and 5 negative for MUC1) were loaded with MUC1 antigens or tumor lysate and used for therapeutic vaccination. After vaccination, all the MUC1-positive patients acquired antigen-specific immunity whereas only 1 case with MUC1-negative cancer showed the specific immunity. Clinically, marked effects such as reduction in tumor sizes or tumor marker levels or disappearance of malignant pleural effusion were observed in 7 of the 9 MUC1-positive cases. However, MUC1-negative patients did not respond to DC vaccines, with the exception of 1 case with MAGE3-positive lung cancer. Survival of MUC1-positive patients was significantly prolonged in comparison with MUC1-negative patients (mean survival: 16.75 versus 3.80 months, p=0.0101). These data suggest that MUC1 is sufficiently immunogenic to elicit strong anti-tumor immunity as a tumor antigen and that DC vaccines targeting MUC1 are useful for immunotherapy of cancer.