Night Work And Risk Of Breast Cancer Defined By Receptor Status: The CECILE Study

Emilie CORDINA-DUVERGER, INSERM, France
CORDINA-DUVERGER E. 1 , KOUDOU Y. 1 , TRUONG T. 1 , ARVEUX P. 2 , KERBRAT P. 3 , FLORENCE M. 1 , GUENEL P. 1

1 Université Paris-Saclay, Univ. Paris-Sud, UVSQ, INSERM, CESP Center for research in Epidemiology and Population Health, U1018, Cancer & Environment Group, Villejuif, France
2 Centre Georges-Francois Leclerc, Registre des tumeurs gynecologiques, Dijon, France
3 Centre Eugene Marquis, Rennes, France

Purpose:
In 2007, volume 98 of the IARC monographs concluded that “shift work that involves circadian disruption” was probably carcinogenic to humans (group 2A). Since the publication of the monograph about fifteen epidemiological studies on night shift work and breast cancer have been published with mixed results. Only few studies however have investigated shift work in relation to breast cancer subtypes defined by Estrogen (ER) or Progesterone (PR) receptor and Human Epidermal growth factor Receptor 2 (HER-2) status. 
Methods:
We explored the association of night work with breast cancer subtypes, defined by ER, PR and HER2 status in a case-control study in France including 975 cases and 1317 controls. Night work was defined as work schedule covering at least the entire time span from 11:00 pm to 5:00 am. Odds ratios (OR) contrasting women who had ever vs never worked at night were calculated using logistic regression models adjusting for potential confounders.
 
​Results:
The association of night work with breast cancer was stronger for ER, PR and HER2-positive tumors (OR 1.49, 1.48 and 1.91, respectively) than in the ER, PR and HER2-negative counterparts (OR 0.86, 1.12, 1.56). Stratification by menopausal status showed that these associations were restricted to premenopausal women (OR 2.04, 1.98, 2.80, respectively). The odds ratio for the ER or PR-positive and HER2-positive subtype of breast cancer in premenopausal women was 3.30 (95%CI 1.42-7.67).
 Conclusions:
This study provides evidence that night work might be associated with specific subtypes of breast cancer, and supports findings in other studies. The strongest association was seen in premenopausal women for the breast cancer combining positive hormone receptors (ER+ or PR+) and HER2+.

Funding Source:
National Institute of Cancer (INCa), Fondation de France, French Agency for Environmental and Occupational Health Safety (AFSSET), French National Research Agency (ANR), Ligue contre le Cancer