Finding a cure for cancer is unarguably one of the biggest medical challenges that we face. But what if we could find a way to prevent cancer before it even starts? In this special extended edition of the Big Questions Podcast, we chat to Professor Sarah Blagden, an experimental oncologist at the University of Oxford, and Anna Fry, who has the cancer predisposing condition Lynch Syndrome - putting her at increased risk of developing colorectal and other cancers. Sarah explains how clinical trials of vaccines targeting 'pre-cancer' could revolutionise the fight against cancer, beginning with those at greatest risk.