Induced abortions and the risk of all cancers combined and site-specific cancers in Shanghai

Abortion and Female Cancer Risks among Women Aged 20 to 45 Years: A 10-Year Longitudinal Population-Based Cohort Study in Taiwan

BACKGROUND

Female cancers, including breast, cervical, uterine, and ovarian cancer, remain among the ten most common cancers among women worldwide, but the relationship between female cancers and abortion from previous studies is inconsistent. This study aimed to investigate risks of incident female cancers among women aged 20 to 45 years who underwent abortion in Taiwan compared with those who did not.

METHOD

A longitudinal observational cohort study was conducted using three nationwide population-based databases in Taiwan, focusing on 20- to 45-year-old women, with 10 years of follow-up. Matched cohorts were identified with propensity score 1-to-3 matching between 269,050 women who underwent abortion and 807,150 who did not. Multivariable Cox proportional hazard modeling was used for analysis after adjusting for covariates including age, average monthly payroll, fertility, diabetes mellitus, polycystic ovarian syndrome, endometrial hyperplasia, endometriosis, hormone-related drugs, and Charlson comorbidity index.

RESULTS

We found lower risk of uterine cancer (hazard ratio [HR]: 0.77, 95% CI: 0.70-0.85) and ovarian cancer (HR: 0.81, 95% CI: 0.75-0.88), but no significant difference in risk of breast cancer or cervical cancer, among matched abortion compared with non-abortion cohorts. Regarding subgroup analysis, cervical cancer risk was higher for parous women who underwent abortion, and uterine cancer risk was lower for nulliparous women who underwent abortion compared with non-abortion groups.

CONCLUSIONS

Abortion was related to lower uterine and ovarian cancer risk but was not associated with risks of incident breast cancer or cervical cancer. Longer follow-up may be necessary to observe risks of female cancers at older ages.

Expanding Our Understanding of Ovarian Cancer Risk: The Role of Incomplete Pregnancies

BACKGROUND

Parity is associated with decreased risk of invasive ovarian cancer; however, the relationship between incomplete pregnancies and invasive ovarian cancer risk is unclear. This relationship was examined using 15 case-control studies from the Ovarian Cancer Association Consortium (OCAC). Histotype-specific associations, which have not been examined previously with large sample sizes, were also evaluated.

METHODS

A pooled analysis of 10 470 invasive epithelial ovarian cancer cases and 16 942 controls was conducted. Odds ratios (ORs) and 95% confidence intervals (CIs) for the association between incomplete pregnancies and invasive epithelial ovarian cancer were estimated using logistic regression. All models were conditioned on OCAC study, race and ethnicity, age, and education level and adjusted for number of complete pregnancies, oral contraceptive use, and history of breastfeeding. The same approach was used for histotype-specific analyses.

RESULTS

Ever having an incomplete pregnancy was associated with a 16% reduction in ovarian cancer risk (OR = 0.84, 95% CI = 0.79 to 0.89). There was a trend of decreasing risk with increasing number of incomplete pregnancies (2-sided Ptrend < .001). An inverse association was observed for all major histotypes; it was strongest for clear cell ovarian cancer.

CONCLUSIONS

Incomplete pregnancies are associated with a reduced risk of invasive epithelial ovarian cancer. Pregnancy, including incomplete pregnancy, was associated with a greater reduction in risk of clear cell ovarian cancer, but the result was broadly consistent across histotypes. Future work should focus on understanding the mechanisms underlying this reduced risk.

Menstrual and reproductive history and use of exogenous sex hormones and risk of thyroid cancer among women: a meta-analysis of prospective studies

PURPOSE

Thyroid cancer has a higher incidence in women than in men, and it has been hypothesized that hormonal factors may explain such disparity. We performed a meta-analysis of observational prospective studies to investigate the association between menstrual and reproductive variables and exogenous hormone use and the risk of thyroid cancer among women.

METHODS

We calculated summary relative risks and 95% confidence intervals (95% CI) using random effect models.

RESULTS

Overall, 5,434 thyroid cancer cases from twenty-four papers were included. Increasing age at first pregnancy/birth (SRR 1.56, 95% CI 1.01-2.42) and hysterectomy (SRR 1.43, 95% CI 1.15-1.78) were associated with thyroid cancer risk. Women that were in menopause at enrolment had a reduced thyroid cancer risk (SRR 0.79, 95% CI 0.62-1.01). No other menstrual, reproductive, and hormonal variable was associated with thyroid cancer risk.

CONCLUSIONS

Menstrual and reproductive factors may play a role in the etiology of thyroid cancer, possibly through the mediation of estrogen receptors.

Reproductive factors and risk of lung cancer in female textile workers in Shanghai, China

PURPOSE

Hormonal factors may play a role in the development of lung cancer in women. This study examined the relationship between lung cancer and reproductive factors in a large cohort of women, most of whom never smoked (97%).

METHODS

A cohort of 267,400 female textile workers in Shanghai, China, enrolled in a trial of breast self-examination provided information on reproductive history, demographical factors, and cigarette smoking at enrollment in 1989-91. The cohort was followed until July of 2000 for incidence of lung cancer; 824 cases were identified. Hazard ratios (HR) and 95% confidence intervals (CI) associated with selected reproductive factors were calculated using Cox proportional hazards modeling, adjusting for smoking, age, and also parity when relevant.

RESULTS

Nulliparous women were at increased risk compared to parous women (HR = 1.33, 95% CI 1.00-1.77). Women who had gone through menopause at baseline were at increased risk compared to women of the same age who were still menstruating. Risk was higher in women with a surgical menopause (HR = 1.64, 95% CI 0.96-2.79) than in those with a natural menopause (HR = 1.35, 95% CI 0.84-2.18), and risk was highest in those postmenopausal women with a hysterectomy and bilateral oophorectomy at baseline (HR = 1.39, 95% CI 0.96-2.00), although the risk estimates were not statistically significant.

CONCLUSIONS

These results support experimental data that demonstrate a biological role for hormones in lung carcinogenesis.

Incomplete pregnancy and risk of ovarian cancer: results from two Australian case-control studies and systematic review

Although full-term pregnancies reduce the risk of ovarian cancer, it has not been conclusively established whether incomplete pregnancies also influence risk. We investigated the relationship between a history of incomplete pregnancy and incident epithelial ovarian cancer among over 4,500 women who participated in two large Australian population-based case-control studies in 1990-1993 and 2002-2005. They provided responses to detailed questions about their reproductive histories and other personal factors. Summary odds ratios (OR) and confidence intervals (CI) derived for each study using the same covariates were aggregated. We found no significant associations between the number of incomplete pregnancies and ovarian cancer, for parous (OR = 0.98, 95% CI: 0.89, 1.08) or nulliparous (OR = 1.06, 95% CI: 0.75, 1.48) women, nor for the number of spontaneous or induced abortions and ovarian cancer for parous women (OR = 0.95, 95% CI 0.82, 1.09; OR = 1.08, 95% CI: 0.86, 1.36) or nulliparous women (OR = 1.2, 95% CI: 0.6, 2.4; OR = 0.8, 95% CI: 0.47, 1.38), respectively. A systematic review of 37 previous studies of the topic confirmed our findings that a history of incomplete pregnancy does not influence a woman's risk of epithelial ovarian cancer.

A case-control study of reproductive factors, female hormone use, and risk of pancreatic cancer

Findings from several previous studies that have assessed the relation of reproductive factors and female hormone use to the risk of pancreatic cancer are inconclusive. The authors examined the association between reproductive factors and the use of oral contraceptives and postmenopausal hormone therapy to the risk of pancreatic cancer among 284 patients with pancreatic cancer and 1,096 controls using data from the hospital-based Case-Control Surveillance Study. Older age at first pregnancy and long-duration oral contraceptive use were associated with an increased risk of pancreatic cancer: the odds ratio was 2.0 (95% CI: 1.1-3.3) for first birth at age 30 or older compared with before age 20 (p for trend = 0.042) and 2.0 (95% CI: 1.0-4.0) for ten or more years of use of oral contraceptive use relative to no-use (p for trend < 0.01). Risk of pancreatic cancer risk was not associated with postmenopausal female hormone use. The findings suggest that increased exposure to estrogen during the reproductive years may play a role in the development of pancreatic cancer in women. Further studies are needed to confirm the findings.

Beyond parity: association of ovarian cancer with length of gestation and offspring characteristics

Women with higher parity have a lower risk of ovarian cancer possibly because of pregnancy hormones, but the specific effect of different pregnancy hormones on ovarian cancer risk is not clear. Some clarification might be gained by considering situations where hormone levels vary between pregnancies. Study participants from an Australian population-based, case-control study of epithelial ovarian cancer (2001-2005) completed a reproductive/lifestyle questionnaire. The authors included 1,203 cases and 1,286 controls with at least 1 birth and, using multiple logistic regression, calculated odds ratios and 95% confidence intervals to investigate the effects of pregnancy-related factors on cancer risk. Women who had 1 or more preterm births had higher risks of ovarian cancer than those who had only full-term births (odds ratio (OR) = 1.48, 95% confidence interval (CI): 1.02, 2.15). The authors also found that bearing only boys was associated with a 2-fold increased risk of mucinous ovarian cancer (OR = 2.19, 95% CI: 1.15, 4.17). There was no association between multiple pregnancy and ovarian cancer (for any multiple pregnancy vs. only singleton pregnancies: OR = 1.22, 95% CI: 0.74, 2.02). The results suggest that pregnancies associated with differing hormonal milieux have different effects on ovarian cancer risk and that some of these associations may vary with histologic subtype.

Breast cancer risk factors in Turkish women--a University Hospital based nested case control study

BACKGROUND

Breast cancer has been increased in developing countries, but there are limited data for breast cancer risk factors in these countries. To clarify the risk for breast cancer among the Turkish women, an university hospital based nested case-control study was conducted.

METHODS

Between January 2000 and December 2006, a survey was prospectively conducted among women admitted to clinics of Istanbul Medical Faculty for examination and/or treatment by using a questionnaire. Therefore, characteristics of patients diagnosed with breast cancer (n = 1492) were compared with control cases (n = 2167) admitted to hospital for non-neoplastic, non-hormone related diseases.

RESULTS

Breast cancer risk was found to be increased in women with age (> or = 50) [95% confidence interval (CI) 2.42-3.18], induced abortion (95% CI 1.13-1.53), age at first birth (> or = 35) (95% CI 1.62-5.77), body mass index (BMI > or = 25) (95% CI 1.27-1.68), and a positive family history (95% CI 1.11-1.92). However, decreased breast cancer risk was associated with the duration of education (> or = 13 years) (95% CI 0.62-0.81), presence of spontaneous abortion (95% CI 0.60-0.85), smoking (95% CI 0.61-0.85), breast feeding (95% CI 0.11-0.27), nulliparity (95% CI 0.92-0.98), hormone replacement therapy (HRT) (95% CI 0.26-0.47), and oral contraceptive use (95% CI 0.50-0.69). On multivariable logistic regression analysis, age (> or = 50) years (OR 2.61, 95% CI 2.20-3.11), induced abortion (OR 1.66, 95% CI 1.38-1.99), and oral contraceptive use (OR 0.60, 95% CI 0.48-0.74) were found to be associated with breast cancer risk as statistically significant independent factors.

CONCLUSION

These findings suggest that age and induced abortion were found to be significantly associated with increased breast cancer risk whereas oral contraceptive use was observed to be associated with decreased breast cancer risk among Turkish women in Istanbul.

Oral contraceptives and the risk of all cancers combined and site-specific cancers in Shanghai

From 1998 to 1991, an in-person baseline interview was administered to approximately 267,400 female textile workers in Shanghai, China. The cohort was followed until July 2000 for incident cancer cases. Incidence rate ratios (RR) for 12 types of cancers in users of oral contraceptives (OCs) were calculated using Cox Proportional Hazards analysis. There was a reduced risk of uterine corpus cancer for women who had ever used OCs (RR = 0.68, 95% CI = 0.45-1.04) and a trend of decreasing risk with increasing duration of use (p = 0.015). There was an increased risk of colon cancer in women who had used OCs for 10 years or more (RR = 1.56, 95% CI = 1.01-2.40) and an increased risk of rectal cancer in women who had ever used OCs (RR = 1.31, 95% CI = 0.98-1.75), with a trend of increasing risk with increasing duration of use (p = 0.017), but these associations may have been due to uncontrolled confounding by physical activity or other non-causal factors. No associations were observed between OCs and the risk of all cancers combined or for any of the nine other cancers. It is unlikely that the use of OCs has contributed to the temporal trends in cancer incidence in China in recent decades.

Reproductive factors and pancreatic cancer risk: a Norwegian cohort study

A cohort of 63 090 Norwegian women born 1886–1928 was followed more than 38 years, and relations between reproductive factors and risk of pancreatic cancer were explored; 449 cases were recorded at ages 50–89 years. Age at menopause showed a moderately positive association with risk (rate ratio (RR)=1.08 per 2 years delay in menopause; 95% confidence interval (CI)=1.00–1.17). Neither parity nor duration of breastfeeding showed significant associations with risk after adjusting only for demographic factors. With mutual adjustment, however, parity became positively associated (RR=1.13 per delivery; 95% CI=1.05–1.22) while duration of breastfeeding was inversely associated (RR=0.87 per 12 months; 95% CI=0.78–0.97). These associations lessened in magnitude with increasing age, and were essentially absent above age 80 years. Risk was raised among women reporting at least one abortion, but no trend was seen with number of abortions. Together with previous studies, the findings raise questions about the role of chance, but do not exclude hormonal factors related to breastfeeding and pregnancy from affecting pancreatic cancer risk.

Monthly injectable contraceptives and the risk of all cancers combined and site-specific cancers in Shanghai

PURPOSE

The risk of 12 types of cancer in relation to use of monthly injectable contraceptives was assessed in a prospective study in Shanghai, China.

METHODS

From 1989 to 1991, an in-person interview was administered to 267,400 female textile workers to ascertain information on risk factors for breast cancer, contraceptive use and induced abortions. The cohort was followed until July 2000 for incident cancer cases. Cox proportional hazards analysis was used to calculate incidence rate ratios for specific types of cancer in women who ever had used monthly injectable contraceptives and by length of use.

RESULTS

There was a reduced risk of uterine corpus cancer for women who had ever used monthly injectable contraceptives. No association was observed between the use of monthly injectable contraceptives and the risk of all cancers combined and for any of the 11 other cancers considered.

CONCLUSION

There appears to be no evidence of an increased risk of cancer after exposure to monthly injectable contraceptives in our study.