The geographical distribution of cancer.

STUDY of the geographical distribution of cancer has long been recognized to be one way of obtaining clues to its causation, and a great deal of work has been carried out to determine the incidence of different types of cancer in different parts of the world. Detailed incidence rates have been obtained for more than fifty populations, either by national or regional cancer registries or by special investigations in selected areas. Many of the results have been published in book form or government reports which are not readily accessible, and others have been published only in summary or in such a way that comparison with other sets of data is difficult or impossible. To help overcome this, incidence data for thirtyfour populations in twenty-three countries have recently been brought together in comparable form in a single volume by the International Union against Cancer (1966). Incidence data, however, constitute only part of the available evidence. Mortality statistics have been published for the principal types of cancer in fortyeight countries and in the urban areas of the fifteen Soviet republics (World Health Organization, 1966; Segi and Kurihara, 1964; Merkova, Tserkovnogo, and Kaufman, 1963) and, in some circumstances, these can provide useful indicators of incidence. Indeed, in some areas in which cancer registration is incomplete, mortality can provide a better indication of incidence than the official " incidence statistics ", particularly for cancers whose fatality is high or for which it is possible to obtain a reasonably accurate indication of the proportion that are not directly responsible for causing death. Finally, there is an immense number of clinical and pathological records. Few can be used to provide reliable estimates of incidence, but, in exceptional circumstances, they provide a clear indication of a situation that is qualitatively different in different parts of the world (as with Burkitt's lymphoma and Kaposi's sarcoma). The extent of the variation in cancer incidence has been reviewed and the geographical distribution of six types of cancer has been published in map form elsewhere (Doll, 1967 and 1968). Corresponding numerical data and incidence rates for ten other types of cancer are given here.