Tubal sterilization and breast cancer incidence: results from the cancer prevention study II nutrition cohort and meta-analysis

Non-genetic factors and breast cancer: an umbrella review of meta-analyses

BACKGROUND

Previous research has found associations between various non-genetic factors and breast cancer (BrCa) risk. This study summarises and appraises the credibility of the available evidence on the association between non-genetic factors and BrCa risk.

METHODS

We conducted an umbrella review of meta-analyses. Medline, Scopus, and the Cochrane databases were systematically searched for meta-analyses examining non-genetic factors and BrCa incidence or mortality. The strength of the evidence was graded in four categories (i.e., weak, suggestive, highly suggestive, convincing).

RESULTS

A total of 781 meta-analyses from 280 publications were evaluated and graded. We included exposures related to anthropometric measurements, biomarkers, breast characteristics and diseases, diet and supplements, environment, exogenous hormones, lifestyle and social factors, medical history, medication, reproductive history, and pregnancy. The largest number of examined associations was found for the category of diet and supplements and for exposures such as aspirin use and active smoking. The statistically significant (P-value < 0.05) meta-analyses were 382 (49%), of which 204 (53.4%) reported factors associated with increased BrCa risk. Most of the statistically significant evidence (n = 224, 58.6%) was graded as weak. Convincing harmful associations with heightened BrCa risk were found for increased body mass index (BMI), BMI and weight gain in postmenopausal women, oral contraceptive use in premenopausal women, increased androstenedione, estradiol, estrone, and testosterone concentrations, high Breast Imaging Reporting and Data System (BIRADS) classification, and increased breast density. Convincing protective factors associated with lower BrCa risk included high fiber intake and high sex hormone binding globulin (SHBG) levels while highly suggestive protective factors included high 25 hydroxy vitamin D [25(OH)D] levels, adherence to healthy lifestyle, and moderate-vigorous physical activity.

CONCLUSIONS

Our findings suggest some highly modifiable factors that protect from BrCa. Interestingly, while diet was the most studied exposure category, the related associations failed to reach higher levels of evidence, indicating the methodological limitations in the field. To improve the validity of these associations, future research should utilise more robust study designs and better exposure assessment techniques. Overall, our study provides knowledge that supports the development of evidence-based BrCa prevention recommendations and guidance, both at an individual level and for public health initiatives.

TRIAL REGISTRATION

PROSPERO CRD42022370675.

A systematic review and meta-analysis on tubal ligation and breast cancer risk

BACKGROUND

Based on previous studies, it has been hypothesized that tube sterilization may be associated with a lower risk of breast cancer. This study aims to investigate the relationship between tubal ligation and the risk of breast cancer through a systematic review and meta-analysis.

METHODS

In this systematic review and meta-analysis, PubMed/Medline, Web of Science, Scopus, and Google Scholar were searched for relevant non randomized studies published up to November 2020. Then, we screened the papers to include the eligible papers in the meta-analysis. Finally, we pooled the extracted results of individual studies to estimate the summary effect size. All analyses were done using Stata software version 13 (Stata Corp, College Station, TX).

RESULTS

Four hundred sixty-four papers were retrieved from PubMed/Medline (160), Scopus (165), and Web of Science (139), and 21 papers from Google Scholar and manual search of references in selected full texts. After the removal of duplicates and screening of the papers, 11 articles (6 cohort and 5 case-control study) were included in the final analysis. The results of cohort (RR = 0.99, 95% CI = 0.97-1.0, I² = 21.1%) and case control studies (OR = 0.87, 95% CI = 0.62-1.12, I² = 88.9%) revealed that tubal ligation was not significantly associated with breast cancer risk.

CONCLUSION

According to our findings, tubal ligation cannot be considered as a risk factor associated with breast cancer risk.

Recent developments have made female permanent contraception an increasingly attractive option, and pregnant women in particular ought to be counselled about it

BACKGROUND

Despite the increased prevalence of reversible contraception, global unintended pregnancy rates are stable. Mistakes, method failures, side effects, alcohol, stock-outs, fears, costs, delays, myths, religious interference, doctors with other priorities, traditions and lack of health professionals may all factor in. Yet these unintended pregnancies - nearly a hundred million annually - cause much individual suffering, and in the long run, can aggravate conflicts, poverty, forced emigration and climate change. Presently, non-poor women postpone childbearing because of longer educational trajectories and careers. Sterilisations are therefore less often regretted or coerced. For poor-resourced women with a completed family, an unwanted pregnancy often has serious consequences, including crossing the (extreme) poverty line in the wrong direction, choosing an unsafe abortion, or even death. Caesarean sections (CSs), which currently stand at around 23 million annually, are increasing. On an "intention-never-to-become-pregnant-again" analysis, choosing a partial, and even more so a total bilateral tubectomy to be implemented during an - anyway performed - CS is by far the most reliable and safe contraceptive choice compared to meaning to start female or male sterilisation or any other contraceptive method later, and it reduces the chance of a future ovarian carcinoma substantially. CSs make subsequent pregnancies more dangerous. Simultaneously, they provide convenient, potentially cost-free opportunities for voluntary permanent contraception (PC): particularly important if there is no guaranteed future access to reliable contraception, safe abortion and well-supervised labour.

PARTIAL SOLUTION

Millions of women are within reach of attaining freedom from the "tyranny of excessive fertility" when they have a CS. Therefore, any woman who might conceivably be of the firm opinion that her family will be (over) completed after delivery should antenatally have "what if you have a CS" counselling to assess whether she would like a tubectomy/ligation. Yet many are not provided with this option: leading to frequent regret, more often than having been giving that choice would.

CONCLUSION

Withholding antenatal counselling about the option of PC for in case the delivery might become a CS is very prevalent, yet often more medically risky, and morally questionable than when, even in labour, a doctor sometimes decides in the absence of earlier counselling, considering numerous factors, to provide the choice to undergo a concurrent sterilisation if s/he is convinced that would be in the patient's best interest.

Tubal ligation and incidence of 26 site-specific cancers in the Million Women Study

BACKGROUND

Tubal ligation is known to be associated with a reduction in ovarian cancer risk. Associations with breast, endometrial and cervical cancers have been suggested. We investigated associations for 26 site-specific cancers in a large UK cohort.

METHODS

Study participants completed a questionnaire on reproductive and lifestyle factors in 1996-2001, and were followed for cancer and death via national registries. Using Cox regression models, we estimated adjusted relative risks (RRs) for 26 site-specific cancers among women with vs without tubal ligation.

RESULTS

In 1 278 783 women without previous cancer, 167 430 incident cancers accrued during 13.8 years' follow-up. Significantly reduced risks were found in women with tubal ligation for cancers of the ovary (RR=0.80, 95% CI: 0.76-0.85; P<0.001; n=8035), peritoneum (RR=0.81, 0.66-0.98; P=0.03; n=730), and fallopian tube (RR=0.60, 0.37-0.96; P=0.04; n=168). No significant associations were found for endometrial, breast, or cervical cancers.

CONCLUSIONS

The reduced risks of ovarian, peritoneal and fallopian tube cancers are consistent with hypotheses of a common origin for many tumours at these sites, and with the suggestion that tubal ligation blocks cells, carcinogens or other agents from reaching the ovary, fallopian tubes and peritoneal cavity.

Tubal ligation in relation to menopausal symptoms and breast cancer risk

Background:

Local inflammation after tubal ligation may affect ovarian function and breast cancer risk.

Methods:

We analysed tubal ligation, menopausal characteristics, and breast cancer risk in the Sister Study cohort (N=50 884 women).

Results:

Tubal ligation was associated with hot flashes (hazard ratio (HR) 1.09; 95% confidence interval (CI): 1.06–1.12) but not menopausal age (HR 0.99; 95% CI: 0.96–1.02). Tubal ligation did not have an impact on breast cancer overall (HR 0.95; 95% CI: 0.85–1.06), but had a suggested inverse relation with oestrogen receptor+/progesterone receptor+ invasive tumours (HR 0.84; 95% CI: 0.70–1.01), possibly because of subsequent hysterectomy/bilateral oophorectomy.

Conclusion:

Tubal ligation does not influence overall breast cancer risk.

Invited commentary: reproductive organ surgeries and breast cancer risk--apples, oranges, or fruit cocktail?

Case-control and cohort studies are almost always complicated by nonrandom exposure allocation, which must be minimized in the design and analysis phases. Tubal sterilization is a common gynecological procedure that may be associated with other reproductive organ surgeries, which in turn may be associated with breast cancer risk. In this issue of the Journal, Gaudet et al. (Am J Epidemiol. 2013;177(6):492-499) argue successfully that tubal sterilization is unassociated with breast cancer risk. Scrutiny of the heterogeneous studies included in their meta-analysis underscores the role of confounding and effect modification in observational epidemiologic studies. Specifically, tubal sterilization is unassociated with breast cancer risk, but either oophorectomy or hysterectomy, or both, and the timing of these procedures warrant careful consideration in the design, analysis, and interpretation of observational research on reproductive factors.