Incidence and Mortality Rates for Leukemia and Lymphoma

Abstract

T HE VARIOUS FORMS of leukemia and lymphoma are generally considered progressive and uniformly fatal. It may therefore be expected that, in any given population, incidence rates for these diseases will be close to the corresponding mortality rates. However, as shown by Shimkin (1) and others, this is not generally true. Table 1 shows the incidence rates for leukemia and lymphoma reported by two large-scale cancer surveys and one cancer register and compares them with mortality rates reported in the same areas and for the sanle years. All three incidence rates for leukemia and two of the three rates for lymphoma were substantially higher than the corresponding mortality rates. An incidence-mortality ratio of, for example, 1.50 (equivalent to a mortality-incidence ratio of 0.67) seems to imply that one-third of the patients reported to have leukemia or lymphoma are not dying of these diseases. This is not necessarily true. For chronic disease registers receiving both case reports and death certificates, there are several ways in which a person could be included in incidence data for any given disease but could be omitted from the corresponding mortality data, or vice versa.