Estimation of incidence of human leukaemia subtypes in an urban African population

A rough estimate of the incidence rates (IR) of human leukaemia subtypes is provided for Ibadan, a large urban centre in the south-western rain-forest area of Nigeria. In view of the inavailability of recent census figures, the current population sizes of various 5-year age groups were projected from those of the last reliable census held in 1963, using various recommendations from national and international bodies on population changes in the area. On comparing the IR for the leukaemia subtypes in Ibadan subjects with those of Black and White Americans, we found no striking difference in chronic myeloid leukaemia for the 3 population groups. Leukaemia IR in Ibadan was low for all subtypes after 70 years, probably because of the thinness of the population after that age. IR of acute lymphoblastic leukaemia (ALL) in the first two quiquennia was low while that of acute myelogenous leukaemia (AML) in the second quinquennium was high in Ibadan compared with Black and White US subjects. IR of AML in Ibadan as well as in Black and White US subjects showed a stepwise increase in the 5-year age groups between 15 and 69 years, but unlike the observation in Americans, ALL was not observed after 40 years of age in Ibadan. Though the method used to estimate the leukaemia incidence rate in Ibadan was crude, it did reveal remarkable differences from those of inhibitants of a developed country like the US. These differences are believed to be related to environmental influences.