Katie M. O’Brien

The independent and joint associations of hysterectomy and uterine fibroids or endometriosis with ovarian cancer incidence: results from a US-based cohort

Abstract Uterine fibroids and endometriosis may be associated with an increased risk of ovarian cancer. Less is known about the role of hysterectomy in these associations. We estimated the independent and joint associations of hysterectomy, fibroids, and endometriosis with ovarian cancer incidence in the prospective Sister Study cohort (2003-2009). We used time-varying Cox proportional hazards models to estimate covariate-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs). By the end of follow-up, 34% of 40 928 eligible participants had fibroids, 13% had endometriosis, and 7% had both. A total of 274 women developed ovarian cancer during follow-up (median = 12.3 years). In mutually adjusted models, fibroids (HR, 1.65; 95% CI, 1.28-2.12) and possibly endometriosis (HR, 1.16; 95% CI, 0.82-1.63) were positively associated with ovarian cancer. Hysterectomies (20% of participants) were also positively associated with ovarian cancer (HR, 1.29; 95% CI, 0.95-1.74). There was some evidence that hysterectomies may mitigate ovarian cancer risk among women with fibroids (HR, 0.83; 95% CI, 0.56-1.24) but not among women with endometriosis (HR, 1.20; 95% CI, 0.65-2.22). Identifying these joint associations adds to our understanding of ovarian cancer etiology and may help inform decisions about how women with fibroids, endometriosis, and hysterectomies are treated and surveilled for ovarian cancer. This article is part of a Special Collection on Gynecological Cancer.

Pubertal Timing and Incident Ovarian Cancer in the Sister Study Cohort

Abstract Background: Pubertal milestones such as menarche (first period) and thelarche (onset of breast development) are markers of hormonal changes that may be relevant to the hormonal etiology of ovarian cancer. Prior studies of the association between age at menarche and ovarian cancer risk have been inconsistent, whereas age at thelarche has not been examined in relation to ovarian cancer incidence. Methods: With data from 40,809 women in the Sister Study, we used multivariable-adjusted Cox proportional hazards regression to estimate HRs and 95% confidence intervals (CI) for associations of self-reported ages at thelarche and menarche with incident ovarian cancer, both overall and by histotype. Results: During a median follow-up of 13.3 years, 291 women reported a diagnosis of ovarian cancer. Ages at thelarche (HR = 0.94; 95% CI, 0.87–1.02 per 1-year older) and menarche (HR = 0.99; 95% CI, 0.91–1.07 per 1-year older) were not associated with ovarian cancer overall. Although imprecise, HRs suggested a possible inverse association of ages at thelarche (HR = 0.71; 95% CI, 0.48–1.04) and menarche (HR = 0.79; 95% CI, 0.59–1.04) with the incidence of clear-cell tumors. Conclusions: Ages at thelarche and menarche were not associated with ovarian cancer incidence overall. Impact: Though our results do not provide clear evidence of associations of pubertal timing with ovarian cancer incidence, possible associations of earlier thelarche and menarche with increased incidence of ovarian clear-cell carcinoma may warrant further investigation, especially considering secular trends toward earlier thelarche.

Intimate Care Products and Incidence of Hormone-Related Cancers: A Quantitative Bias Analysis

PURPOSE Intimate care products may contain substances associated with increased risk of hormone-related cancers. The relationship between genital talc use and ovarian cancer, in particular, has been well studied, but concerns about recall bias and exposure misclassification have precluded conclusions. We examined the association between intimate care products and female hormone–related cancers, accounting for potential biases, using data from a US-based cohort study. METHODS The Sister Study enrolled 50,884 women who had a sister with breast cancer. Data on genital talc use and douching were collected at enrollment (2003-2009) and follow-up (2017-2019). We used Cox proportional hazards models to estimate hazard ratios (HRs) for associations between intimate care product use and breast, ovarian, and uterine cancers. To account for potential exposure misclassification and recall bias, we conducted quantitative bias analyses under various exposure reassignment assumptions. RESULTS Across considered scenarios, 41%-64% of participants douched and 35%-56% used genital talc. In models adjusted for exposure misclassification, genital talc use was positively associated with ovarian cancer (HR range, 1.17-3.34) Frequent douching and douching during young adulthood were positively associated with ovarian cancer, but neither douching nor talc was associated with breast or uterine cancer. Differential reporting of talc use by cases and noncases likely produces positive biases, but correcting for error still resulted in HRs above 1.0. For example, HR, 1.40 (95% CI, 1.04 to 1.89) when 25% of exposed cases and 10% of unexposed noncases had talc status reassigned. CONCLUSION Although results show how differential recall would upwardly bias estimates, corrected results support a positive association between use of intimate care products, including genital talc, and ovarian cancer.

Ovarian Cancer Risk Factor Associations by Primary Anatomic Site: The Ovarian Cancer Cohort Consortium

Abstract Background: Epithelial ovarian, fallopian tube, and primary peritoneal cancers have shared developmental pathways. Few studies have prospectively examined heterogeneity in risk factor associations across these three anatomic sites. Methods: We identified 3,738 ovarian, 337 peritoneal, and 176 fallopian tube incident cancer cases in 891,731 women from 15 prospective cohorts in the Ovarian Cancer Cohort Consortium. Associations between 18 putative risk factors and risk of ovarian, peritoneal, and fallopian tube cancer, overall and for serous and high-grade serous tumors, were evaluated using competing risks Cox proportional hazards regression. Heterogeneity was assessed by likelihood ratio tests. Results: Most associations did not vary by tumor site (Phet ≥ 0.05). Associations between first pregnancy (Phet = 0.04), tubal ligation (Phet = 0.01), and early-adult (age 18–21 years) body mass index (BMI; Phet = 0.02) and risk differed between ovarian and peritoneal cancers. The association between early-adult BMI and risk further differed between peritoneal and fallopian tube cancer (Phet = 0.03). First pregnancy and tubal ligation were inversely associated with ovarian, but not peritoneal, cancer. Higher early-adult BMI was associated with higher risk of peritoneal, but not ovarian or fallopian tube, cancer. Patterns were generally similar when restricted to serous and high-grade serous cases. Conclusions: Ovarian, fallopian tube, and primary peritoneal cancers appear to have both shared and distinct etiologic pathways, although most risk factors appear to have similar associations by anatomic site. Impact: Further studies on the mechanisms underlying the differences in risk profiles may provide insights regarding the developmental origins of tumors arising in the peritoneal cavity and inform prevention efforts.

The Risk of Ovarian Cancer Increases with an Increase in the Lifetime Number of Ovulatory Cycles: An Analysis from the Ovarian Cancer Cohort Consortium (OC3)

Abstract Repeated exposure to the acute proinflammatory environment that follows ovulation at the ovarian surface and distal fallopian tube over a woman's reproductive years may increase ovarian cancer risk. To address this, analyses included individual-level data from 558,709 naturally menopausal women across 20 prospective cohorts, among whom 3,246 developed invasive epithelial ovarian cancer (2,045 serous, 319 endometrioid, 184 mucinous, 121 clear cell, 577 other/unknown). Cox models were used to estimate multivariable-adjusted HRs between lifetime ovulatory cycles (LOC) and its components and ovarian cancer risk overall and by histotype. Women in the 90th percentile of LOC (>514 cycles) were almost twice as likely to be diagnosed with ovarian cancer than women in the 10th percentile (<294) [HR (95% confidence interval): 1.92 (1.60–2.30)]. Risk increased 14% per 5-year increase in LOC (60 cycles) [(1.10–1.17)]; this association remained after adjustment for LOC components: number of pregnancies and oral contraceptive use [1.08 (1.04–1.12)]. The association varied by histotype, with increased risk of serous [1.13 (1.09–1.17)], endometrioid [1.20 (1.10–1.32)], and clear cell [1.37 (1.18–1.58)], but not mucinous [0.99 (0.88–1.10), P-heterogeneity = 0.01] tumors. Heterogeneity across histotypes was reduced [P-heterogeneity = 0.15] with adjustment for LOC components [1.08 serous, 1.11 endometrioid, 1.26 clear cell, 0.94 mucinous]. Although the 10-year absolute risk of ovarian cancer is small, it roughly doubles as the number of LOC rises from approximately 300 to 500. The consistency and linearity of effects strongly support the hypothesis that each ovulation leads to small increases in the risk of most ovarian cancers, a risk that cumulates through life, suggesting this as an important area for identifying intervention strategies. Significance: Although ovarian cancer is rare, risk of most ovarian cancers doubles as the number of lifetime ovulatory cycles increases from approximately 300 to 500. Thus, identifying an important area for cancer prevention research.

Modification of the Association Between Frequent Aspirin Use and Ovarian Cancer Risk: A Meta-Analysis Using Individual-Level Data From Two Ovarian Cancer Consortia

PURPOSE Frequent aspirin use has been associated with reduced ovarian cancer risk, but no study has comprehensively assessed for effect modification. We leveraged harmonized, individual-level data from 17 studies to examine the association between frequent aspirin use and ovarian cancer risk, overall and across subgroups of women with other ovarian cancer risk factors. METHODS Nine cohort studies from the Ovarian Cancer Cohort Consortium (n = 2,600 cases) and eight case-control studies from the Ovarian Cancer Association Consortium (n = 5,726 cases) were included. We used Cox regression and logistic regression to assess study-specific associations between frequent aspirin use (≥ 6 days/week) and ovarian cancer risk and combined study-specific estimates using random-effects meta-analysis. We conducted analyses within subgroups defined by individual ovarian cancer risk factors (endometriosis, obesity, family history of breast/ovarian cancer, nulliparity, oral contraceptive use, and tubal ligation) and by number of risk factors (0, 1, and ≥ 2). RESULTS Overall, frequent aspirin use was associated with a 13% reduction in ovarian cancer risk (95% CI, 6 to 20), with no significant heterogeneity by study design ( P = .48) or histotype ( P = .60). Although no association was observed among women with endometriosis, consistent risk reductions were observed among all other subgroups defined by ovarian cancer risk factors (relative risks ranging from 0.79 to 0.93, all P-heterogeneity > .05), including women with ≥ 2 risk factors (relative risk, 0.81; 95% CI, 0.73 to 0.90). CONCLUSION This study, the largest to-date on aspirin use and ovarian cancer, provides evidence that frequent aspirin use is associated with lower ovarian cancer risk regardless of the presence of most other ovarian cancer risk factors. Risk reductions were also observed among women with multiple risk factors, providing proof of principle that chemoprevention programs with frequent aspirin use could target higher-risk subgroups.

Use of personal care product mixtures and incident hormone-sensitive cancers in the Sister Study: A U.S.-wide prospective cohort

Personal care products (PCPs), a source of endocrine-disrupting chemical exposure, may be associated with the risk of hormone-sensitive cancers. Few studies have investigated associations for PCP use with the incidence of hormone-sensitive cancers or considered the joint effect of multiple correlated PCPs. We examined associations between frequently used, or "everyday", PCPs and incident cancers of the breast, ovary, and uterus with a fucus on the joint effect of multiple product exposure. Sister Study participants (n=49 899) self-reported frequency of use in the year before enrollment (2003-2009) for 41 PCPs. Using five-level frequency categories based on questionnaire options, hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated for the associations between multiple PCP use and incident breast, ovarian, and uterine cancer using quantile-based g-computation with Cox proportional hazards regression as the underlying model. Multiple PCP use was examined using groupings (beauty, hygiene, and skincare products) determined by both a priori knowledge and Spearman correlation coefficients for co-occurring product use. Associations between individual PCPs and the three cancers were also examined using Cox proportional hazards models coupling with Benjamini-Hochberg procedure for multiple comparisons. Over an average of 11.6 years, 4 226 breast, 277 ovarian, and 403 uterine cancer cases were identified. Positive associations were observed between the hygiene mixture and ovarian cancer (HR=1.35, 95%CI=1.00, 1.83) and the beauty mixture with postmenopausal breast cancer (HR=1.08, 95%CI=1.01, 1.16). Additionally, we observed an inverse association between the skincare mixture and breast cancer (HR=0.91, 95%CI=0.83, 0.99). No significant associations were observed for individual products after corrected for multiple comparison. Findings from this multi-product, joint-effect approach contribute to the growing body of evidence for associations between PCPs and breast cancer and provides novel information on ovarian and uterine cancer.