Re: "Night-Shift Work and Breast Cancer Risk in a Cohort of Chinese Women"

Erren, Thomas C.; Pinger, Andreas; Morfeld, Peter

doi:10.1093/aje/kwq277

Cited by 3 publications

(2 citation statements)

References 7 publications

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“…This is particularly true in a research field such as shift work and cancer which does already attract considerable public interest. Second, case-control studies which obtain exposure information via questionnaires rather than being based on (rather) unbiased industry-records [26] can be conducted in a relatively fast fashion. However, such studies may be prone to critical self-selection bias among the controls and to recall bias among the cases.…”

Section: Discussionmentioning

confidence: 99%

Shift work, cancer and "white-box" epidemiology: Association and causation

Erren

2010

Epidemiol Perspect Innov

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This commentary intends to instigate discussions about upcoming epidemiologic research, and its interpretation, into putative links between shift work, involving circadian disruption or chronodisruption [CD], and the development of internal cancers.In 2007, the International Agency for Research on Cancer (IARC) convened an expert group to examine the carcinogenicity of shift work, inter alia characterized by light exposures at unusual times. After a critical review of published data, the following was stated: "There is sufficient evidence in experimental animals for the carcinogenicity of light during the daily dark period (biological night)". However, in view of limited epidemiological evidence, it was overall concluded: "Shiftwork that involves circadian disruption is probably carcinogenic to humans (Group 2A)".Remarkably, the scenario around shift work, CD and internal cancers provides a unique case for "white-box" epidemiology: Research at many levels - from sub-cellular biochemistry, to whole cells, to organs, to organisms, including animals and humans - has suggested a series of quite precise and partly related causal mechanisms. This is in stark contrast to instances of "black box" or "stabs in the dark" epidemiology where causal mechanisms are neither known nor hypothesized or only poorly defined. The overriding theme that an adequate chronobiological organization of physiology can be critical for the protection against cancer builds the cornerstone of biological plausibility in this case.We can now benefit from biological plausibility in two ways: First, epidemiology should use biologically plausible insights into putative chains of causation between shift work and cancer to design future investigations. Second, when significant new data were to become available in coming years, IARC will re-evaluate cancer hazards associated with shift work. Biological plausibility may then be a key viewpoint to consider and, ultimately, to decide whether (or not) to pass from statistical associations, possibly detected in observational studies by then, to a verdict of causation.In the meantime, biological plausibility should not be invoked to facilitate publication of epidemiological research of inappropriate quality. Specific recommendations as to how to design, report and interpret epidemiological research into biologically plausible links between shift work and cancer are provided.Epidemiology is certainly a poor toolfor learning about the mechanismby which a disease is produced,but it has the tremendous advantagethat it focuses on the diseases and the deathsthat actually occur,and experience has shown that it continues to be second to none asa means of discovering linksin the chain of causationthat are capable of being broken.-Sir Richard Doll [1]

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Section: Discussionmentioning

confidence: 99%

Shift work, cancer and "white-box" epidemiology: Association and causation

Erren

2010

Epidemiol Perspect Innov

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“…That the study by Kubo et al . used industry‐based shift work data documented in an independent fashion (when compared with questionnaire or interview information) is a further asset 8 . Taken together, as the “remarkably high quality exposure information” on a “counterclockwise three‐shift system” constitutes a key facet of this study, it would have been a candidate for inclusion in the abstract.…”

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confidence: 99%

Counter‐clockwise shift‐work and prostate cancer: Putting pieces in the puzzle

2011

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The retrospective cohort study 1 of prostate cancer risks among rotating shift-workers published by Dr Kubo et al. can be relevant for several reasons. In 2006, Kubo et al. were the first to investigate possibly elevated prostate cancer risks in male shift workers.2 At that time, their prospective cohort study evinced that rotating-shift workers were significantly at risk for prostate cancer. A little later, the 2007 International Agency for Research on Cancer (IARC) classification of "shift-work that involves circadian disruption is probably carcinogenic to humans" (Group 2A) 3 provided further impetus for observational studies into shift work and cancer.From scientific and public health viewpoints, this classification of a "probable" nexus of widespread and inevitable shift work, on the one hand , and epidemic and , thus far, mainly unpreventable cancers such as breast and prostate cancer, on the other, left us with a puzzle. What, if any, shift work conditions might increase the risk of what, if any, cancer? The IARC experts based their evaluation of epidemiological data almost exclusively on breast cancer in female nurses and flight personnel, 3 and an IARC press release called for studies of "potential risks in other professions and for other cancers". 4 In this vein, Dr Kubo et al. now contribute to filling in information regarding two important pieces of this puzzle.First, with regard to end-points, this study adds to the few studies that addressed prostate cancer. 2,5,6 Second , with regard to exposures, it appears that this study is unique insofar as it focused on counter-clockwise shift regimens. Although prior studies based on "shift work" status might have included such shift organization, we simply don't know when, and there could have been mixes of clockwise and counter-clockwise shifts. That the direction of shift rotation might be important information to consider has been pointed out by Foster and Kreitzman, who emphasized that it is not settled empirically whether forward or backward shift rotation is less favorable for shift workers. 7 It is indeed conceivable that, possibly depending on the shift workers' chronotypes, some individuals might do better with counter-clockwise rather than clockwise rotation of shifts. Importantly, therefore, we need factual data on the possible effects of counter-clockwise shifts. That the study by Kubo et al. used industry-based shift work data documented in an independent fashion (when compared with questionnaire or interview information) is a further asset. 8 Taken together, as the "remarkably high quality exposure information" on a "counterclockwise three-shift system" constitutes a key facet of this study, it would have been a candidate for inclusion in the abstract.A final reason as to why this study can be relevant is the fact that its results are now available in the public scientific domain. The authors point out that "some increase in the risk of prostate cancer for shift workers was observed , although the result was not statistically signific...

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Pronk

Shu

et al. 2010

American Journal of Epidemiology

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Re: "Night-Shift Work and Breast Cancer Risk in a Cohort of Chinese Women"

Cited by 3 publications

References 7 publications

Shift work, cancer and "white-box" epidemiology: Association and causation

Shift work, cancer and "white-box" epidemiology: Association and causation

Counter‐clockwise shift‐work and prostate cancer: Putting pieces in the puzzle

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