Cancer as a continuum: a literature review and a biological interpretation

Basic research shows that the genetic control of development cannot fully explain the phenotypic plasticity of humans and other metazoans. This challenges some tenets of the conventional paradigm of life sciences based on DNA, restoring a role of the environment in biological processes like the regulation of development, cell differentiation and disease. The environment — in a broad sense — affects biological phenotypes throughout the entire lifespan and can induce cancer, its progression and recurrence as well as its reversal. This is very important in cancer epidemiology as it implies that environmental exposures can be considered both as risk (or protective) and prognostic factors. This review integrates information from epidemiologic and biological research. We studied the impact of hazardous and protective exposures, lifestyles, and diet on the survival of patients who had been diagnosed with cancer.We selected studies from two digital databases, using a few combinations of key terms, namely overall survival, cancer-specific survival, recurrence and quality of life (QoL). Survival and/or recurrence were expressed as hazard or risk ratios, as second cancer diagnosis and as indicators of QoL such as performance status. We found 53 articles indicating that risk and protective factors can also influence prognosis after cancer diagnosis. Cigarette smoking and, among protective factors, diet and physical activity are the exposures most frequently investigated after a diagnosis of cancer.