Cohort Designs In Cancer Research

Cancer has a complex etiology; an interaction of environmental, lifestyle and genetic factors isrequired to cause cancer. In the last decades, using cohort design; one of the fundamental studydesigns in Epidemiology, researchers were able to provide key insights into environmental,lifestyle, and genetic determinants of this disease and its outcomes. A cohort study begins with agroup of individuals who are identified to have a certain exposure and then the group is followedprospectively over time in order to obtain the information on occurrence of the disease of interest.Therefore, cohort studies are considered as a fundamental study design in cancer epidemiologybecause they allow the calculation of the basic epidemiologic measures of association; incidenceand mortality rates, with different types of exposure. Cancer epidemiology cohorts (CECs) arecategorized into 1) longitudinal observational studies of healthy individuals, which are followed upuntil disease occurrence and 2) cancer survivor cohorts which provide information on cancerprognosis and survivorship. The former provides key evidence for the development of riskprediction models, prevention strategies, and guidelines and the latter provides evidence for theefficacy of many treatment and health policy interventions. More recently, in-depth analyses ofgene-environment interactions and also patient cohorts come to interest to better examinedeterminants of clinical, genomic, and lifestyle factors of cancer development as well as cancerprognosis and survival. Although cohort studies have advantages in cancer epidemiology, there aresome limitations such as loss to follow up due to a decade or more follow-up period, a need forample fund and strong project management as well as larger sample sizes. This design is also notsuitable for rare cancers.