Human Evolutionary Carcinogenesis and Effects of Demographic and Epidemiologic Transitions in Low- and Middle-Income Countries.

Abstract

ABSTRACT INTRODUCTION In many countries cancer is or threatens to become the leading cause of death, although incidence and mortality rates differ between high-income and low- and middle-income countries. Developments in evolutionary biology have revealed that carcinogenesis is even more complex than previously thought. Several theories attempt to integrate the various existing points of view about what is known to date. OBJECTIVE Analyze and explain the main current theories of carcinogenesis and explore their possible application to understanding the demographic and epidemiologic transitions’ effects on cancer population dynamics in low- and middle-income countries. EVIDENCE ACQUISITION A systematic literature review was carried out in MEDLINE (via PubMed), SCOPUS (via Science Direct) and SciELO. Consistency and quality of evidence in articles reviewed were taken into account; we excluded studies with consistency levels of IV and V, and those with limited or insufficient quality of evidence. DEVELOPMENT Human evolution has led to a type of life history characterized by numerous tradeoffs with oncogenic implications. Cultural coevolution and socioeconomic development have affected cancer population dynamics. Several theories explain carcinogenesis from an ecological and evolutionary perspective, among them somatic mutation, adaptive oncogenesis, life history theories, and the Noble and Hochberg model. The human environmental effect on cancer risk is manifested in the influence of demographic and epidemiologic transitions in low- and middle-income countries, where cancer represents a high disease burden due to the effects of recently introduced environmental factors in native environments, accentuation of adaptive decoupling, and diversification of genetic polymorphisms for cancer susceptibility. CONCLUSIONS The Noble and Hochberg model best explains the population dynamics of cancer in low- and middle-income countries, especially regarding the effects of recently introduced environmental factors on native environments, adaptive decoupling and genetic diversity (manifest in differences in clinical and biological tumor expression by level of economic development), in response to demographic and epidemiologic transitions.