Cancer vaccines: will we ever learn?

Scientists and clinicians engaged in developing therapeutic cancer vaccines cannot be anything other than troubled by the sheer number of Phase III clinical trial failures in the field. Are we inveterate optimists or do we have reason for continuing to plough our lonely furrow? In this perspective article, we answer why Phase III failures have been to the fore and highlight why the field should be optimistic given the knowledge gained from these pioneering studies and our improved understanding of how the immune system interacts with cancer.