Background: Investigations on the effects of malaria infection on cancer mortality are limited except for the incidence of Burkitt's lymphoma (BL) in African children. Our previous murine lung cancer model study demonstrated that malaria infection significantly inhibited tumor growth and prolonged the life span of tumor-bearing mice. This study aims to assess the possible associations between malaria incidence and human cancer mortality.
Methods: We compiled data on worldwide malaria incidence and age-standardized mortality related to 30 types of cancer in 56 countries for the period 1955-2008, and analyzed their longitudinal correlations by a generalized additive mixed model (GAMM), adjusted for a nonlinear year effect and potential confounders such as country's income levels, life expectancies and geographical locations.
Results: Malaria incidence was negatively correlated with all-cause cancer mortality, yielding regression coefficients (log scale) of -0.020 (95%CI: -0.027,-0.014) for men (P < 0.001) and-0.020 (95%CI: -0.025,-0.014) for women (P < 0.001). Among the 29 individual types of cancer studied, malaria incidence was negatively correlated with colorectum and anus (men and women), colon (men and women), lung (men), stomach (men), and breast (women) cancer.
Conclusions: Our analysis revealed a possible inverse association between malaria incidence and the mortalities of all-cause and some types of solid cancers, which is opposite to the known effect of malaria on the pathogenesis of Burkitt's lymphoma. Activation of the whole immune system, inhibition of tumor angiogenesis by Plasmodium infection may partially explain why endemic malaria might reduce cancer mortality at the population level.
Keywords: Cancer mortality; Epidemiological data; Generalized additive mixed model (GAMM); Malaria incidence; Regression analysis.