Increased risk of breast cancer associated with long-term shift work in Canada

Short-term effects of night shift work on breast cancer risk: a cohort study of payroll data

“…Wang et al (28) 16-3.38) and were thus only partly in agreement with our findings (29). ER+/HER2-tumors constituted 88% of the ER+ tumors in this material and the decreased risk we observed for this subtype is not supportive of earlier studies showing associations between night shift work and ER+ tumors (without information on HER2 receptor status) (25)(26)(27)(28). Experimental studies implicate melatonin suppression in HER2+ carcinogenesis (45,46).…”

“…Several epidemiological studies have observed an increased risk of breast cancer following long-term night shift work that we were not able to assess due to lack of work schedule data prior to 2007 (18,25,27,(49)(50)(51)(52). An unknown part of the cohort subjects employed during 2007-2012 were hired prior to 2007 where we have no information on working time.…”

“…This suggests distinct etiologic pathways for breast cancer subtypes and new risk factors may be overseen if this is not accounted for (24). Night shift work has been associated with estrogen receptor positive (ER+) (25)(26)(27)(28)(29), ER- (26,30), progesterone receptor positive (PR+) (26)(27)(28)(29), human epidermal growth factor 2 positive (HER2+) (29,31) and HER2-breast cancer subtypes (29). The strongest association was reported for HER2+ in combination with ER+ or PR+ receptor status (29).…”

Impact of Environmental Contaminants on Breast Cancer / Wpływ Zanieczyszczenia Środowiska Na Raka Piersi

“…Moreover, women with morning preference who worked on night shifts tended to have a higher risk than those with evening preference [297]. Long-term (≥ 30 years) night shift work in a diverse mix of occupations was associated with increased breast cancer risk (OR = 2.21, 95% CI 1.14-4.31) and this association was showing similar results for both health and non-health care workers [304]. Positive association of extended periods of rotating night work and breast cancer risk (more than 30 years of rotating night work) was reported also by Schernhammer et al [301].…”

Response to Ijaz S, et al. “Night-shift work and breast cancer - a systematic review and meta-analysis”

“…Other investigators who have recently published meta-analyses on the same topic (3,4) came to different conclusions regarding the quality of several of the individual studies and the overall result. Finally, a recent case-control study not included in these meta-analyses also gives support to the association between long-term, non-day work and breast cancer risk (5).…”