More than a third of us will suffer from it; one fourth will die of it. Cancer is the number one killer in Canada. However, our understanding of cancer has evolved dramatically over the past 10 years. We look at the principal theories and hypotheses that are revolutionizing our knowledge of this disease. We meet Guy, Agathe, Claude and Denis, four patients suffering from various forms of cancer who confront their illness, a complex and insidious scourge that is increasingly being treated with revolutionary therapies. Four battles waged, and four fates in the balance.