Cancer registries can play an important role in monitoring and evalu- ating the effectiveness of primary prevention measures. As mentioned in Section , trends in cancer incidence can be related to changes over time in exposure to risk factors. Occasionally, when implementation has been confined to one area, comparisons of the changes in the intervention area versus ‘control’ areas may be possible. It should be kept in mind when interpreting such relationships that it takes considerable time (generally decades) for the effect of a change in exposure to be reflected in cancer incidence data
