Shift work and cancer: state of science and practical consequences.

In 2007, an expert Working Group convened by the IARC Monographs Programme concluded that shift work that involves circadian disruption is probably carcinogenic to humans (Group 2A). We scrutinised the epidemiological basis for this conclusion, with a focus on, but not limited to, breast and prostate cancers. We further considered practical consequences for shift workers in our industry against the background of new findings.We carried out a literature search including the epidemiological studies cited by IARC and newer available literature on shift work and cancer.Since the IARC assessment, eleven new studies have emerged, ten of which have already been published, with inconclusive results. Heterogeneity of exposure metrics and study outcomes and emphasis on positive but non-significant results make it difficult to draw general conclusions. Also, several reviews and commentaries, which have been published meanwhile, came to equivocal results. Published evidence is widely seen as suggestive but inconclusive for an adverse association between night work and breast cancer, and limited and inconsistent for cancers at other sites and all cancers combined.At this point in time it can not be ruled out that shift work including night work may increase the risk for some cancers in those who perform it. However, shift schedules can be organised in ways that minimise the associated health risks, and the risks may be further reduced through the implementation of structured and sustained health promotion programs specifically tailored to the needs of shift workers.