IARC confirms night work cancer link
An association between night work and breast and other cancers has been confirmed after a major review by an International Agency for Research on Cancer (IARC) expert group. IARC’s 2007 ‘probably carcinogenic in humans’ Group 2A ranking was challenged in 2016 after an Oxford University study co-financed by the Health and Safety Executive (HSE) and Cancer Research UK (CRUK) concluded “night shift work, including long-term night shift work, has little or no effect on breast cancer incidence.” The paper, which attracted headlines worldwide and whose findings were welcomed by both HSE and CRUK, concluded IARC’s ranking of night work as a ‘probable’ cause of breast cancer in women “is no longer justified.” However, the paper attracted strong criticism and was dismissed as ‘bad science’ by leading work and breast cancer experts (Risks 781). The controversy led IARC, a World Health Organisation (WHO) agency, to convene a ‘Monographs Working Group’ in June 2019, The findings of IARC’s reevaluation, published online this month, rejected the HSE/CRUK study’s conclusions. Instead, the IARC expert group again “classified night shift work as ‘probably carcinogenic to humans’ (Group 2A), on the basis of limited evidence of cancer in humans (for cancers of the breast, prostate, colon, and rectum), sufficient evidence of cancer in experimental animals, and strong mechanistic evidence in experimental animals.” However, unions have expressed concern that the doubt cast on the cancer association by the HSE/CRUK backed paper adversely affected efforts to recognise, address and compensate night-work related breast cancer.
IARC Monographs Volume 124: Night Shift Work, June 2020. Volume 124 webpage. Graveyard shift: Cancer all-clear for night work based on ‘bad science’, warn scientists, Hazards magazine, number 136, December 2016.
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