Occupational exposures and breast cancer among women textile workers in Shanghai

Background: Breast cancer incidence rates have been increasing in China over the past 2 decades. Most studies have focused on reproductive, dietary, and genetic risk factors. Little is known about the contribution of occupational exposures. Methods: We conducted a case-cohort study within a cohort of female textile workers who had participated in a randomized trial of breast self-examination in Shanghai, China. We compared 1709 incident breast cancer cases with an age-stratified reference subcohort (n = 3155 noncases). Cox proportional hazards modeling, adapted for the case-cohort design, was used to estimate hazard ratios for breast cancer in relation to duration of employment in various job processes and duration of exposure to several agents. We also evaluated the associations of cotton dust and endotoxin with breast cancer. Results: Cumulative exposures to cotton dust and endotoxin demonstrated strong inverse gradients with breast cancer risk when exposures were lagged by 20 years (trend P-values < 0.001). We did not observe consistent associations with exposures to electromagnetic fields, solvents, or other chemicals. Conclusion: Endotoxin or other components of cotton dust exposures may have reduced risks for breast cancer in this cohort, perhaps acting at early stages of carcinogenesis. Replication of these findings in other occupational settings with similar exposures will be needed to confirm or refute any hypothesis regarding protection against breast cancer.