ABSTRACT
The initial studies usually focus on differences in the incidence of cancer and mortality between different areas of the world or within countries. These are generally termed ecological or descriptive studies, which may have involved cross-sectional surveys or cancer registration. Cancer registries that are informed of all cancers in their area with a known population can give good incidence and survival data for studying trends over time in registrations, deaths and survival from cancer. Environmental factors can increase the local incidence of cancers. One example is the presence of radon in housing, which is dependent on local geology. High radon levels in a house can increase the risk of lung cancer developing in people living there. Smoking has been implicated as a direct cause or promoter of cancer. The association was first noted for lung cancer, but smoking has since been implicated in many other cancers, including those of the bladder, cervix, oesophagus, mouth, pharynx and larynx.
