Introduction

It is customary to assess the distribution of disease, including cancer, by age, sex, place and time. The most informative estimate of the frequency and distribution of cancer in a population comes from the cancer registry, an organization which measures incidence by recording all newly diagnosed cases of cancer occurring in a defined population. If incidence data are not available, then mortality, the number of persons in a defined population certified as dying from cancer, is used as a surrogate index of the cancer burden. The relation between incidence and mortality varies by cancer site and is influenced by the effectiveness and success of therapy and level of medical services. Many of the issues in measuring human cancer have been summarized by Muir et al. (1987) in CI5V (a commonly used abbreviation for Volume V of the monograph series Cancer Incidence in Five Continents).

The International Classification of Diseases (ICD) of the World Health Organization, now in its ninth revision, is universally used to present cancer occurrence data. The classification is largely organized on an anatomical basis since location influences cancer treatment, histological type and other factors. Indeed, the causal agent often determines the organ involved. A few cancers are primarily classified on histological or cytological criteria rather than anatomical location, e.g. choriocarcinoma, malignant melanoma of skin, malignant lymphomas and leukemia.