Cancer epidemiology is the study of the patterns of cancer occurrence in a population.
It is mainly statistical with its methods and conclusions being expressed in probabilities. The basic function of cancer epidemiology is to describe the occurrence of human cancer. An incidence rate is the probability of an individual in a particular group being diagnosed with cancer within a year. For example, the incidence rate of breast cancer in females in United States in 1990 was 151 per 100,000. For most forms of cancer, the incidence rate increases rapidly with aging.