The reason medicine lacks sufficient preventative interventions is mostly because of the scientific and ethical requirements. Hence manufacturers will likely take years, if ever, to get their research investment back. Peddlers of snake-oil are therefore having a field day promising the moon. Orac gives a detailed explanation of the mechanism involved, and current achievements, by the medical community combatting cancer.
Update. In a new post Orac points out the methods of detecting breast-cancer the scientifically-challenged are introducing.