The Healthy Worker Effect in Cancer Epidemiology

Despite the relationship between work and cancer has received more attention, occupational cancer still often be ignored and underestimated its population and health care burden. This is partly attributable to the fact that the traditional methods for studying cancer in the occupational population can’t evaluate the healthy worker effect (HWE) adequately. The HWE is one of the most wearisome methodological aspects in occupational epidemiological studies, which often take the general population as the reference group. As a result, real excesses in both morbidity and mortality due to occupational exposures might be masked. It has been recognized that the HWE arises from two complementary processes: the selection of healthier workers at hire (healthy worker hire effect); and the interruption, change, or cessation of work by less healthy workers (healthy worker survivor effect). Further, the HWE has been recognized as the source of selection bias for a long time. Some researchers also view the HWE as a source of information bias or confounding bias. For the elimination of the HWE, studies could be designed prospectively with follow-up starting before hire, included lifetime information regarding health events (e.g., age of cancer onset) and occupational history, and needed to take into account exposure windows in relation to the onset of cancer symptoms. The information bias would be minimal if an appropriate reference population with comparable information can be identified. Confounding can be controlled in data analysis. However, researchers still have to notice the HWE when conducting and interpreting the results of cancer epidemiological studies, and clinicians should not rule out the possibility of occupational cancer in patients with an apparently clinical presentation.