Cancer and environment: definitions and misconceptions.

Background: Scientific evidence supports an association between environmental exposures and cancer. However, a reliable estimate for the proportion of cancers attributable to environmental factors is currently unavailable. This may be related to the varying definitions of the term "environment." The current review aims to determine how the reporting of the definition of the environment and of the estimates of environmentally attributable risks have changed over the past 50 years.

Methods: A systematic literature search was performed to retrieve all relevant publications relating to the environment and cancer from January 1960 to December 2010 using PubMed, EMBASE, Scopus, and Web of Science. Definitions of the environment and environmentally attributable risks for cancer were extracted from each relevant publication.

Results: The search resulted in 261 relevant publications. We found vast discrepancies in the definition of the environment, ranging from broad (including lifestyle factors, occupational exposures, pollutants, and other non-genetic factors) to narrow (including air, water, and soil pollutants). Reported environmentally attributable risk estimates ranged from 1% to 100%.

Conclusions: Our findings emphasize the discrepancies in reporting environmental causation of cancer and the limits of inference in interpreting environmentally attributable risk estimates. Rather than achieving consensus on a single definition for the environment, we suggest the focus be on achieving transparency for any environmentally attributable risks.