Shift work and breast cancer among women textile workers in Shanghai, China.

PURPOSE: Although night-shift work has been associated with elevated risk of breast cancer in numerous epidemiologic studies, evidence is not consistent. We conducted a nested case-cohort study to investigate a possible association between shift work including a night shift and risk of breast cancer within a large cohort of women textile workers in Shanghai, China. METHODS: The study included 1,709 incident breast cancer cases and 4,780 non-cases. Data on historical shift work schedules were collected by categorized jobs from the factories, where the study subjects had worked, and then were linked to the complete work histories of each subject. No jobs in the factories involved exclusively night-shift work. Therefore, night shift was evaluated as part of a rotating shift work pattern. Hazard ratios and 95 % confidence intervals were calculated using Cox proportional hazards modeling adapted for the case-cohort design for years of night-shift work and the total number of nights worked. Additionally, analyses were repeated with exposures lagged by 10 and 20 years. RESULTS: We observed no associations with either years of night-shift work or number of nights worked during the entire employment period, irrespective of lag intervals. Findings from the age-stratified analyses were very similar to those observed for the entire study population. CONCLUSIONS: The findings from this study provide no evidence to support the hypothesis that shift work increases breast cancer risk. The positive association between shift work and breast cancer observed in Western populations, but not observed in this and other studies of the Chinese population, suggests that the effect of shift work on breast cancer risk may be different in Asian and Caucasian women.

Occupational exposure to magnetic fields and breast cancer among women textile workers in Shanghai, China.

Exposure to magnetic fields (MFs) is hypothesized to increase the risk of breast cancer by reducing production of melatonin by the pineal gland. A nested case-cohort study was conducted to investigate the association between occupational exposure to MFs and the risk of breast cancer within a cohort of 267,400 female textile workers in Shanghai, China. The study included 1,687 incident breast cancer cases diagnosed from 1989 to 2000 and 4,702 noncases selected from the cohort. Subjects' complete work histories were linked to a job-exposure matrix developed specifically for the present study to estimate cumulative MF exposure. Hazard ratios and 95% confidence intervals were calculated using Cox proportional hazards modeling that was adapted for the case-cohort design. Hazard ratios were estimated in relation to cumulative exposure during a woman's entire working years. No association was observed between cumulative exposure to MFs and overall risk of breast cancer. The hazard ratio for the highest compared with the lowest quartile of cumulative exposure was 1.03 (95% confidence interval: 0.87, 1.21). Similar null findings were observed when exposures were lagged and stratified by age at breast cancer diagnosis. The findings do not support the hypothesis that MF exposure increases the risk of breast cancer.

Mammographic breast density and tolerance for short-term postmenopausal hormone therapy suspension.

BACKGROUND: Breast density tends to decrease when women stop taking hormone therapy (HT). Some women find HT cessation difficult to tolerate, possibly because of fluctuations in endogenous hormone levels and vasomotor symptoms. We hypothesized that women with dense breasts might have lower tolerance for short-term HT suspension than do women with fatty breasts. METHODS: As part of the Radiologic Evaluation And breast Density (READ) trial, we randomly assigned 881 women aged 45-80 with a prior screening (index) mammogram to suspend HT for 1 or 2 months before their next screening (study) mammogram. We measured continuous breast density on index mammograms using computer-assisted thresholding. At study mammograms, women indicated tolerance for stopping HT from 1 (extremely difficult) to 7 (very easy). Using linear regression, we evaluated the association between index breast density and tolerance after cessation, adjusting for age, body mass index (BMI), HT type, randomization group, and vasomotor symptoms. RESULTS: A higher percentage of breast density was associated with lower unadjusted mean tolerance scores (tolerance 4.27, 95% confidence interval [CI] 3.77-4.77 for women with > or =50% density, and 4.73, 95% CI 4.45-5.01 for women with <10% density, not a statistically significant difference). In adjusted analyses, neither percent breast density nor dense breast area was associated with tolerance for HT suspension. CONCLUSIONS: Although HT use affects breast density, tolerance for suspending HT is not associated with breast density. Women with dense breasts have the greatest potential for decreases in density after HT cessation; they should tolerate stopping HT as well as women with fatty breasts.

Physical activity, physical exertion, and miscarriage risk in women textile workers in Shanghai, China.

BACKGROUND: Strenuous occupational physical activity and physical demands may be risk factors for adverse reproductive outcomes. METHODS: A retrospective study in the Shanghai, China textile industry study collected women's self-reported reproductive history. Occupational physical activity assessment linked complete work history data to an industry-specific job-exposure matrix. Odds ratios (OR) and 95% confidence intervals (CI) were estimated by multivariate logistic regression for the first pregnancy outcome and utilized generalized estimating equations to consider all pregnancies per woman. RESULTS: Compared with women employed in sedentary jobs, a reduced risk of miscarriage was found for women working in jobs with either light (OR 0.18, 95% CI: 0.07, 0.50) or medium (OR 0.24, 95% CI: 0.08, 0.66) physical activity during the first pregnancy and over all pregnancies (light OR 0.32, 95% CI: 0.17, 0.61; medium OR 0.43, 95% CI: 0.23, 0.80). Frequent crouching was associated with elevated risk (OR 1.82, 95% CI: 1.14, 2.93; all pregnancies per woman). CONCLUSIONS: Light/medium occupational physical activity may have reduced miscarriage risk, while specific occupational characteristics such as crouching may have increased risk in this cohort.

Short-term hormone therapy suspension and mammography recall: a randomized trial.

BACKGROUND: Without population-based evidence, some clinicians recommend short-term suspension of hormone therapy to improve the performance of mammography. Hormone therapy increases breast density, and abnormal screening mammograms are more common among women with denser breasts and among women using hormone therapy. OBJECTIVE: To test whether 1 to 2 months of hormone therapy suspension before screening mammography decreases additional mammographic imaging (recall) in women age 45 to 80 years. DESIGN: 3-group randomized, controlled trial. SETTING: Integrated health plan in western Washington from 2004 to 2007. PATIENTS: 1704 women age 45 to 80 years who used hormone therapy at their most recent screening (index) mammography, were due for screening (study) mammography, and were still using hormone therapy. INTERVENTION: Block random assignment (by breast density and hormone therapy type) to no hormone therapy suspension (n = 567) or suspension for 1 month (n = 570) or 2 months (n = 567) before study mammography. One blinded expert radiologist interpreted all mammograms. MEASUREMENTS: Recall was the primary outcome, and change in mammographic breast density (percentage and dense area) between the index and study mammograms was the secondary outcome. RESULTS: Mammography recall rates were 11.3% (61 of 542 women in the no-suspension group), 12.3% (50 of 478 women in the 1-month suspension group), and 9.8% (44 of 451 women in the 2-month suspension group). No subgroups were identified in which brief suspension of hormone therapy resulted in decreased mammography recall. With suspension, decreases in percentage of breast density were orderly and statistically significant: 0.1% (no-suspension group), -0.9% (1-month suspension group), and -1.5% (2-month suspension group). Similar ordered decreases were observed for dense area. Women in the suspension groups experienced increased menopause symptoms. LIMITATIONS: Results can only be generalized to women age 45 to 80 years who have used hormone therapy for at least 1 year and will consider short-term suspension; most eligible women (61%) declined participation. Mammography recall was determined by 1 expert radiologist. CONCLUSION: Brief hormone therapy suspension was associated with small changes in breast density and did not affect recall rates. No evidence supports short-term hormone therapy suspension before mammography.

Occupational risk factors for endometrial cancer among textile workers in Shanghai, China.

OBJECTIVE: A case-cohort study was conducted to investigate associations between occupational exposures and endometrial cancer nested within a large cohort of textile workers in Shanghai, China. METHODS: The study included 176 incident endometrial cancer cases diagnosed from 1989 to 1998 and a randomly-selected age-stratified reference subcohort (n = 3,061). Study subjects' complete work histories were linked to a job-exposure matrix developed specifically for the textile industry to assess occupational exposures. Hazard ratios (HR) and 95% confidence intervals were calculated using Cox proportional hazards modeling adapted for the case-cohort design, adjusting for age at menarche and a composite variable of gravidity and parity. RESULTS: An increased risk of endometrial cancer was detected among women who had worked for > or =10 years in silk production (HR = 3.8, 95% CI 1.2-11.8) and had exposure to silk dust (HR = 1.7, 95% CI 0.9-3.4). Albeit with few exposed women (two cases and eight subcohort women), there was a 7.4-fold increased risk associated with > or =10 years of silica dust exposure (95% CI 1.4-39.7). CONCLUSIONS: The findings suggest that some textile industry exposures might play a role in endometrial carcinoma and should be further replicated in other occupational settings.

Occupational exposures and ovarian cancer in textile workers.

BACKGROUND: Occupational risk factors for ovarian cancer have been investigated only to a limited extent. We conducted a case-cohort study to examine associations between occupational exposures and ovarian cancer in the textile industry. METHODS: We compared 261 incident ovarian cancer cases diagnosed between 1989 and 1998 with an age-stratified reference subcohort (n = 3199) from a cohort of 267,400 textile workers in Shanghai, China. Occupational exposures were assessed by job-exposure matrices designed for the textile industry, and estimates of quantitative cotton dust and endotoxin. We calculated hazard ratios (HRs) and 95% confidence intervals (CIs) with Cox proportional hazards modeling adapted for the case-cohort design. RESULTS: A decreased risk of ovarian cancer was associated with ever having worked in cotton manufacturing production (HR = 0.7; 95% CI = 0.4-1.0). An increased risk was associated with ever having worked in textile finishing (2.1; 0.9-5.0). We found an increasing risk of ovarian cancer associated with cumulative exposure to silica dust (for <10 years exposure, HR = 6.8 [CI = 0.6-76]; for > or =10 years, 5.6 [1.3-23.6]), although these results are based on only 8 exposed subcohort women (0.3%) and 4 cases (1.3%). We also detected inverse risk gradients for cumulative exposures to endotoxin when exposures were lagged by 20 years (in highest quartile, HR = 0.6 [CI = 0.4-1.1]). CONCLUSION: Silica dust may increase the risk of ovarian cancer, and cotton dust and endotoxin may reduce risk.

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.

Lung cancer risk among female textile workers exposed to endotoxin.

BACKGROUND: Reduced risk of lung cancer among workers in the cotton textile industry has been observed since the 1970s. Bacterial endotoxin, a contaminant of raw cotton fiber and cotton dust, has been proposed as a protective agent that may act through the innate and acquired immune systems. We examine the association between endotoxin exposure and lung cancer risk in a cohort of female textile workers. METHODS: We conducted a case-cohort study nested within a cohort of 267,400 female textile workers in Shanghai, China. We compared the cumulative exposure histories of 628 case patients diagnosed with incident lung cancer from January 1, 1989, through December 31, 1998, with those of a lung cancer-free reference subcohort of 3184 workers who were frequency matched by 5-year age-groups to all cancer patients in the cohort. Cumulative endotoxin exposure for all participants was based on historic measurements and on additional measurements for this study. Relative risks and 95% confidence intervals (CIs) were estimated by hazard ratios (HRs) from Cox proportional hazards models. We conducted exposure-response trend analyses by use of cumulative exposures with lag times of 0, 5, 10, 15, or 20 years to account for disease latency. All analyses controlled for age and smoking status. All statistical tests were two-sided. RESULTS: Cumulative exposure to endotoxin was strongly, statistically significantly, and inversely associated with lung cancer risk. The inverse trend was greatest with a 20-year lag time, for which highest endotoxin exposure was associated with a statistically significantly 40% less risk of lung cancer (HR = 0.60, 95% CI = 0.43 to 0.83; P(trend) across quintiles = .002) than non-exposure. From a reported population rate of lung cancer among women in Shanghai of 19.1 per 100,000 for the year 2000 and the estimated reduction in risk of lung cancer observed for 20 years of endotoxin exposure in this population of workers, the incidence of lung cancer in this cohort was reduced by approximately 7.6 per 100,000 (range = 3.2-10.9 per 100,000). CONCLUSIONS: Long-term and high-level exposure to endotoxin, compared with no exposure, appears to be associated with a reduced risk of lung cancer in this cohort.