Epidemiological patterns of leukaemia in 184 countries: a population-based study.

BACKGROUND: Leukaemia is a heterogeneous group of haemopoietic cancers that comprises a number of diverse and biologically distinct subgroups. We examine the leukaemia burden worldwide and highlight the distinct incidence patterns in order to elucidate explanatory factors that may support preventive measures and health resource planning. We aimed to estimate the global burden of leukaemia incidence according to the four major subtypes stratified by age and sex.
METHODS: In this population-based study, we assessed leukaemia incidence for the major subtypes using the Cancer Incidence in Five Continents Volume X (CI5-X), which includes data from 290 cancer registries in 68 countries covering the diagnostic period 2003-07, for all ages and both sexes. We then extracted counts and incidence rates in 184 countries for the year 2012 from IARC's GLOBOCAN database of national estimates. We calculated age-specific incidence rates per 100 000 person-years and age-standardised rates (ASRs) using the world standard population by country, sex, age group, and where applicable, by major subtypes. We excluded from all analyses registries for which the total number of leukaemia cases was less than 100 or the proportion of microscopically verified (MV%) cases was less than 80% (2572 cases).
FINDINGS: 717 863 cases between 2003-07 were included in this analysis. More than 350 000 new leukaemia cases were estimated in 2012. We observed substantial variation in incidence between and within world regions. The highest leukaemia incidence rates for both sexes were estimated in Australia and New Zealand (ASR per 100 000 11·3 in males and 7·2 in females), Northern America (10·5 in males and 7·2 in females), and western Europe (9·6 in males and 6·0 in females), and the lowest was in in western Africa (1·4 in males and 1·2 in females). Rates were generally higher in males than females with an overall male to female ratio of 1·4. In children, acute lymphoblastic leukaemia was the main subtype in all studied countries in both sexes, and characterised by a bimodal age-specific pattern. The subtype distribution was more diverse in adults, with a relatively higher proportion of chronic lymphocytic leukaemia in most European and North American countries, whereas rates of acute lymphoblastic leukaemia remained relatively high among adults in selected South American, Caribbean, Asian, and African populations.
INTERPRETATION: Geographical disparities in leukaemia might partly be explained by quality of, and access to, health systems linked to resource levels, although there is probably a role for aetiological factors, including gene-environment interactions. The observed bimodal pattern could be due to different risk factors affecting different ages, and might include a genetic component. FUNDING: European Commission's FP-7 Marie Curie Actions-People-COFUND.