(1) The primary prostate cancer treatment involves androgen deprivation therapy, with or without chemotherapy. Immunotherapy has emerged as a promising strategy against cancer due to its ability to modulate the immune system, overcome immune evasion, and stimulate the attack on tumor cells. Thus, this review urges an exploration of the underlying mechanisms to validate the efficacy and safety of dendritic cell immunotherapy for prostate cancer treatment. (2) An extensive literature search identified 45 eligible studies in PubMed, Web of Science, SCOPUS, and Embase databases. Phase I and II clinical trials and in vitro studies (PROSPERO registration number CRD42024538296) were analyzed to extract information on patient selection, vaccine preparation, treatment details, and disease progression. (3) Despite significant variability in vaccine development and treatment protocols, vaccines were shown to induce satisfactory immune responses, including T-cell activation, increased CD4 and CD8 cell populations, upregulated expression of HLA-A2 and HLA-DR, enhanced migratory capacity of dendritic cells, and elevated interferon levels. Cytokine responses, particularly involving Interleukin 10 (IL-10) and Interleukin 12 (IL-12), varied across studies. Immunotherapy demonstrated potential by eliciting positive immune responses, reducing PSA levels, and showing an acceptable safety profile. However, side effects such as erythema and fever were observed. (4) The analyzed treatments were well-tolerated, but variability in clinical responses and side effects underscores the need for further research to optimize the efficacy and safety of this therapeutic approach.