In Reply

Shift Work and Cancer: The Evidence and the Challenge by Prof. Dr. med. Thomas C. Erren, Puran Falaturi, PD Dr. rer. medic. Peter Morfeld, Prof. Dr.-Ing. Peter Knauth, Prof. Dr. rer. nat. Dr. h. c. mult. Russel J. Reiter, Prof. em. Dr. med. Claus Piekarski in volume 38/2010

Dr Behrens and colleagues mention further pathophysiological mechanisms that may contribute to the development of cancer via chronodisruption. The complements are appropriate. Following a reviewer’s suggestion, we focused on epidemiology in our review. However, mechanistic details are included in the cited publications.

IARC places considerable weight on biological plausibility in their preamble to the „IARC Monographs on the Evaluation of Carcinogenic Risks to Humans“ (1). Ultimately, however, epidemiological studies will have to show whether what appears biologically plausible is indeed relevant for female and male shift workers. Methodologically, the plethora of mechanistic ideas offers a unique situation with regard to considerations of causality such as undertaken by IARC in October of 2007. Indeed, in this important research area one can refer to „white-box” epidemiology (2): a multitude of mechanisms of action are “waiting to be considered” to interpret associations, possibly observed in epidemiological studies in coming years, as being causal and relevant (3).

We agree with our colleagues’ expectations: shift work and chronodisruption will be an important research field for occupational epidemiology and occupational science. The National Cohort Study appears to be an appropriate means to provide insights into chronodisruption, due to different shift regimens, and possible links with cancer.

Overall, it is our expectation that coming years will bring numerous epidemiological studies regarding shift work, chronodisruption and cancer which also consider the pathophysiological mechanisms mentioned by Dr. Behrens et al. The primary objective must be to have high quality observational studies; it must be avoided that qualitatively inferior studies will be published by invoking the suggestive biological plausibility of the investigated relationships.

DOI: 10.3238/arztebl.2011.0008b

Prof. Dr. med. Thomas C. Erren, MPH

Puran Falaturi

PD Dr. rer. medic. Peter Morfeld

Prof. Dr.-Ing. Peter Knauth

Prof. Dr. rer. nat. Dr. h. c. mult. Russel J. Reiter

Prof. em. Dr. med. Claus Piekarski

On behalf of the authors:

Prof. Dr. med. Thomas C. Erren, MPH

Institut und Poliklinik für Arbeitsmedizin,

Umweltmedizin und Präventionsforschung

der Universität zu Köln

Kerpener Str. 62

50937 Köln, Germany

until January 2011: Visiting Scholar; School of Public Health

University of California, Berkeley

Conflict of interest statement
The authors of both contributions declare that no conflict of interest exists according to the guidelines of the International Committee of Medical Journal Editors.

References

1. International Agency for Research on Cancer: Preamble to the IARC Monographs (amended January 2006).

2. Erren TC, Bjerregaard P, Cocco P, Lerchl A, Verkasalo P: Re: „Invited commentary: electromagnetic fields and cancer in railway workers“. Am J Epidemiol 2001; 154: 977–9.

3. Rothman KJ, Greenland S, Lash TL: Modern epidemiology. 3 rd ed. Philadelphia: Lippincott Williams & Wilkins 2008.

4. Erren TC, Falaturi P, Morfeld P, Knauth P, Reiter R, Piekarski C: Shift work and cancer—the evidence and the challenge. Dtsch Arztebl Int 2010; 107(38): 657–62.