Figure 1

An example of evidence for an ‘etiologic field effect’ phenomenon. Smoking has been shown to increase the incidence of colorectal cancer displaying CpG island methylator phenotype, microsatellite instability, and BRAF mutation, as well as the incidence of synchronous colorectal cancers. Smoking, as an etiologic exposure, creates a field effect manifest as altered colonic tissue microenvironment. Microenvironmental change induced by smoking promotes carcinogenesis via specific pathways resulting in synchronous tumors with shared molecular features. As one might expect of an etiologic field, somatic alterations (such as CpG island methylator phenotype, microsatellite instability, and BRAF mutation) are absent from non-neoplastic tissue within the field.