Do the characteristics of health systems influence cancer outcomes? Although caveats are required when undertaking international comparisons of both health systems and cancer outcomes, observed differences cannot solely be explained by data problems or economic development. Health systems can influence cancer outcomes through three mechanisms: coverage, innovation, and quality of care. First, in countries where population coverage is incomplete, patients may find certain services excluded or face substantial copayments or deductibles. Second, there are variations in the rate at which innovative treatments are introduced, reflecting in particular the need for publicly funded health systems to compare costs and benefits of increasingly expensive treatments given demands for other treatments. Third, systematic differences in quality of care (early diagnosis, timely and equitable access to specialist care, and existence of systematic coordination between these activities) may lead to variations in cancer outcomes.