Therapeutic cancer vaccines are an attractive pharmaceutical technology for their potential to selectively kill tumor cells, which should result in improved clinical response without the adverse effects of chemotherapy, surgery or radiotherapy. Furthermore, vaccine-elicited immunity could permanently prevent disease recurrence. Despite the technology platform being essentially unproven, therapeutic cancer vaccines are now a commercial reality ndash; with three approved in various countries.Essentially, there are two types of cancer vaccine: those based on whole tumor cells and those based on specific antigens. They can be further classified into autologous (patient-specific) or allogeneic (nonpatient-specific) vaccines. For several reasons, most researchers now favor antigen-specific approaches, although whole-cell vaccines are still being investigated. Development of cancer vaccines presents significant challenges ndash; including overcoming immune tolerance of tumor cells, identifying appropriate tumor antigens and eliciting potent immune responses without triggering autoimmunity. These challenges have not yet been met, with virtually every promising vaccine tested in randomized phase III trials failing to show efficacy. The only glimmer of hope is that some vaccines have had significant benefit in patients with certain characteristics.Despite the failures, many therapeutic cancer vaccines are coming down the pipeline. Approximately a dozen candidates are currently in pivotal clinical trials with biotech and pharmaceutical companies. Melanoma is the leading indication, with five vaccines in phase III trials. Numerous other candidate vaccines are at earlier stages of clinical development, both with companies and non-commercial organizations. However, development of cancer vaccine technology is limited by an incomplete understanding of tumor immunology, among other factors. Ongoing basic research may enable better vaccines to be designed, but the current state of the field suggests that a truly potent therapeutic cancer vaccine is still years, or even decades away. In the short term, the most likely scenario is that cancer vaccines with modest efficacy will be used in combination with current therapies in specific subsets of patients.
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