Shift work and cancer: the evidence and the challenge.

BACKGROUND: In 2007, the International Agency for Research on Cancer (IARC) classified shift work with circadian disruption or chronodisruption as a probable human carcinogen. Short-term disturbances of biological 24-hour-rhythms following exposures to light and darkness at unusual times are well-known as "jet-lag" and "shift-lag" symptoms. However, that chronic disturbances or disruptions of timely sequenced circadian rhythms (chronodisruption) should contribute to long-term developments of cancer is a relatively new concept. This review provides background and practical information with regard to the open question "does shift-work cause cancer?" METHODS: Overview on the basis of a selective literature search via Medline and ISI Web of Knowledge until 2009 from the viewpoints of occupational medicine, epidemiology, chronobiology, and occupational science. RESULTS: The postulated causal links between shift-work and cancer in humans are biologically plausible in the light of experimental findings, but to date we lack epidemiological studies which could describe or exonerate risks in humans. Monetary compensation has already been paid for such cases in at least one country (Denmark). In Germany, however, according to the applicable law, a new occupational disease can only be recognized when certain conditions for the recognition of "general scientific merit" have been met. We present the current state of knowledge regarding prevention. CONCLUSION: While causal links between shift-work and cancer developments are not established, future shift-work planning should pay more attention to insights from occupational medicine, chronobiology, and occupational science.

Research into the chronodisruption-cancer theory: the imperative for causal clarification and the danger of causal reductionism.

A cascade of investigations into the validity of the chronodisruption-cancer theory (CD-CT), proposed 2008 in Neuroendocrinology Letters as a synthesis of abundant experimental and tantalizing - but still limited - epidemiological data, can be expected in coming years. In view of the possible public health relevance of the suggested links between chronodisruption, defined as the disruption of the temporal organization or order of biological rhythmicity over days and seasons, and the development of disease, including cancer, we provide practical aspects which should be considered for the planning, conduct and the very interpretation of such studies. The interrelated considerations address two facets: first, the critical necessity of causal clarification can be evinced appropriately by Poole's earlier contribution to the Journal. Researchers into the validity of the CD-CT should certainly consider Poole's 2002 illustration via causal graphs for shift work, light at night and breast cancer of the subtleties that can arise in the use of exposure surrogates of different kinds. Second, we emphasize the importance of considering the Zeitgeber multiplicity to avoid causal reductionism in epidemiologic - but also other - chronodisruption research.

Epigenetics: origins and implications for cancer epidemiology.

This paper provides information on the evolution of the 'epigenetics' concept since Aristotle and draws attention to the importance of epigenetic implications for cancer epidemiology in the years to come. Clearly, to understand origins of the concept of epigenetics, it is worthwhile to consider historical arguments associated with evolution. Equally clearly, in the last half of the 20th century, great advances in the understanding of epigenetics and, more specifically, great advances in the understanding of epigenetics in cancer have been made. However, reaping the full benefits of epigenetics lies beyond the predominant experimental studies of today. In general, epigenetics opens many doors in the field of cancer, but it also adds another level of complex, inter-related, and multi-dimensional information to research, and to its interpretation. Overall, future cancer studies should consider, or at least be sensitive to, epigenetic effects and mechanisms. Moving the focus beyond 'pristine' inheritance via DNA alone, cancer epidemiology investigating epigenetic exposures such as environmental factors (exposure to heavy metals, air pollution, arsenic and other toxins), dietary patterns (starvation, famine, contamination), and lifestyle habits (smoking, level of physical activity, and BMI) in populations has the prospect to significantly benefit future cancer prevention and treatment schemes.

Research insights and insides:"Science-in-Fiction" as a contribution to the Third Culture Concepts.

Here we suggest to encourage more "Science-In-Fiction" [SIF], a genre which has been explored by Carl Djerassi since the late 1980s with the intent to convey science in writing beyond traditional publication categories and "to smuggle scientific facts into the consciousness of a scientifically illiterate public". In our view, SIF can serve 3 purposes: (a) inform the public at large about scientific findings, ethics and procedures; (b) infuse lay readers with interest in scientific endeavours; (c) enable the general population to better evaluate and judge scientific conduct, results and implications. While it would be desirable to have more scientists write about their own (like Watson and Maguejo) and others' discoveries (like Voltaire and Perutz), this expectation is not realistic. Indeed, some scientists may not want to share and write about their experiences and others simply should not. As one recipe for informing the lay public and instigating interest in research insights and insides, science-in-fiction such as Dr. Djerassi's novels could be written and read. This may contribute to the The Third Culture Concepts envisaged by Snow in the 1960s and elaborated by Brockman in 1995.