Reproducibility of fifteen urinary estrogens and estrogen metabolites over a 2- to 3-year period in premenopausal women

Association between urine and serum estradiol levels in in vitro fertilization cycles

To study the correlation between urine and serum estradiol (E2) controlled ovarian hyperstimulation (COH). This is a cross-sectional analytical study that was conducted in a tertiary care hospital. Seventy-seven urine and blood samplings were collected from infertile women who were treated with COH. An electrochemiluminescent immunoassay was performed to evaluate E2 levels between urine and serum samples on the 6th day and the day of ovarian trigger. In addition, the correlations were evaluated between urine E2 level and number of follicles, retrieved, metaphase II oocytes, and fertilization rate. A sub-analysis was performed for age, responding status and BMI. Seventy-seven infertile women were recruited. The medians of serum and urine E2 level levels on the day 6th of ovarian stimulation were 833.20 pg/ml (IQR; 516.90-1371.00) and 3.67 (IQR; 2.84-4.81), respectively. On the day of ovarian trigger, the median of serum E2 level was 2113.00 pg/ml (IQR; 1382.00-3885.00) and urine E2 level (E2/creatinine) was 6.84 (IQR; 5.34-8.70). The correlation between serum and urine E2 level on day 6th was 0.53 and the day of ovarian trigger was 0.59, p < 0.001. Moreover, the correlations of urine E2 level on the day of ovarian trigger to number of follicles, number of oocytes retrieved, metaphase II oocytes and fertilization rate were 0.57, 0.58, 0.61, and 0.64 (p < 0.001). The urine E2 level was moderately correlated to serum E2, number of follicles growth, oocytes retrieved and fertilization rate.

Temporal reliability of serum soluble and endogenous secretory receptors for advanced glycation end-products (sRAGE and esRAGE) in healthy women

PURPOSE

The soluble receptor for advanced glycation end-products (sRAGE) and endogenous secretory RAGE (esRAGE) have been considered as biomarkers of several chronic diseases. However, the temporal reliability of their concentrations in the circulation is yet to be demonstrated. We evaluated whether a single measurement of serum sRAGE and esRAGE could serve as an estimate for usual serum levels in epidemiologic studies.

METHODS

Serum sRAGE and esRAGE were measured using ELISAs in three yearly samples from 36 participants in the New York University Women's Health Study. The intraclass correlation coefficient (ICC) was used to evaluate temporal reliability.

RESULTS

The intra- and inter-batch coefficients of variation were 3.0% and 14.8% for sRAGE and 6.5% and 34.7% for esRAGE, and decreased to 0.4% and 2.1% for sRAGE and 1.0% and 6.3% for esRAGE after log₂-transformation of the data. On the original scale, the ICCs of a single measurement of serum sRAGE and esRAGE were 0.89 (95% CI 0.82-0.94) and 0.87 (95% CI 0.79-0.93), respectively, and were similar using log₂-transformed data.

CONCLUSION

Our results indicate that a single measurement of serum sRAGE and esRAGE is a sufficiently reliable measure of their usual levels that can be used in epidemiologic studies.

Estrogen Metabolism in Premenopausal Women Is Related to Early Life Body Fatness

Background: Estrogen metabolism in premenopausal women may be related to early life body fatness.Methods: Premenopausal women participating in the Nurses' Health Study II recalled their body fatness at ages 5, 10, and 20 years using a validated 9-level pictogram. Fifteen estrogens and estrogen metabolites (EM) were measured using LC/MS-MS in luteal phase urines from 603 women ages 32-54 years. Geometric means of individual EM, metabolic pathway groups, and pathway ratios were examined by body fatness categories using linear mixed models.Results: Body fatness at each age was inversely associated with adult concentrations of all EM combined, parent estrogens (estrone, estradiol), and the 2-hydroxylation pathway. Women in the top (vs. bottom) category of body fatness at age 10 had 21% lower levels of all EM (Ptrend = 0.003), 24% lower parent estrogens (Ptrend = 0.002), and 36% lower 2-pathway (Ptrend = 0.0003). Body fatness at age 10 was inversely associated with 2-catechols (35% lower, Ptrend = 0.0004) and 2-methylated catechols (30% lower, Ptrend = 0.002). After adjusting for premenopausal body mass index (BMI), these associations remained inverse but were attenuated; only parent estrogens remained statistically significant (21% lower, Ptrend = 0.01). Body fatness at ages 5 and 20 were similarly, but more weakly, associated with estrogen pathways.Conclusions: Estimates of body fatness during early life were inversely associated with premenopausal levels of all EM combined, parent estrogens, and 2-pathway estrogen metabolites. These relationships were not fully explained by adult BMI.Impact: These findings inform investigations of diseases linked to early life body fatness and estrogen metabolism. Cancer Epidemiol Biomarkers Prev; 27(5); 585-93. ©2018 AACR.

Estrogen- and stress-induced DNA damage in breast cancer and chemoprevention with dietary flavonoid

Breast cancer is one of the most commonly diagnosed female cancers and a leading cause of cancer-related death in women. Multiple factors are responsible for breast cancer and heritable factors have received much attention. DNA damage in breast cancer is induced by prolonged exposure to estrogens, such as 17β-estradiol, daily social/psychological stressors, and environmental chemicals such as polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines (HCAs). DNA damage induced by estrogen and stress is an important factor in the pathogenesis and development of breast cancer and is now recognized as a critical provision for chemoprevention of breast cancer. In this review, we summarize the relationships between estrogen- and stress-induced DNA damage with regard to the pathogenesis and development of breast cancer. We also discuss recent investigations into chemoprevention using dietary flavonoids such as quercetin and isoflavones.

CYP3A7*1C allele is associated with reduced levels of 2-hydroxylation pathway oestrogen metabolites

Background:

Endogenous sex hormones are well-established risk factors for breast cancer; the contribution of specific oestrogen metabolites (EMs) and/or ratios of specific EMs is less clear. We have previously identified a CYP3A7*1C allele that is associated with lower urinary oestrone (E₁) levels in premenopausal women. The purpose of this analysis was to determine whether this allele was associated with specific pathway EMs.

Methods:

We measured successfully 12 EMs in mid-follicular phase urine samples from 30 CYP3A7*1C carriers and 30 non-carriers using HPLC-MS/MS.

Results:

In addition to having lower urinary E₁ levels, CYP3A7*1C carriers had significantly lower levels of four of the 2-hydroxylation pathway EMs that we measured (2-hydroxyestrone, P=1.1 × 10⁻¹²; 2-hydroxyestradiol, P=2.7 × 10⁻⁷; 2-methoxyestrone, P=1.9 × 10⁻¹²; and 2-methoxyestradiol, P=0.0009). By contrast, 16α-hydroxylation pathway EMs were slightly higher in carriers and significantly so for 17-epiestriol (P=0.002).

Conclusions:

The CYP3A7*1C allele is associated with a lower urinary E₁ levels, a more pronounced reduction in 2-hydroxylation pathway EMs and a lower ratio of 2-hydroxylation:16α-hydroxylation EMs in premenopausal women. To further characterise the association between parent oestrogens, EMs and subsequent risk of breast cancer, characterisation of additional genetic variants that influence oestrogen metabolism and large prospective studies of a broad spectrum of EMs will be required.

Association of Active and Sedentary Behaviors with Postmenopausal Estrogen Metabolism

PURPOSE

Physical activity may reduce endogenous estrogens, but few studies have assessed effects on estrogen metabolism and none have evaluated sedentary behavior in relation to estrogen metabolism. We assessed relationships between accelerometer-measured physical activity and sedentary behavior and 15 urinary estrogens and estrogen metabolites (EM) among postmenopausal controls from a population-based breast cancer case-control study conducted in Poland (2000-2003).

METHODS

Postmenopausal women (N = 542) were ages 40 to 72 yr and not currently using hormone therapy. Accelerometers, worn for 7 d, were used to derive measures of average activity (counts per day) and sedentary behavior (<100 counts per minute per day). Estrogen metabolites were measured in 12-h urine samples using liquid chromatography-tandem mass spectrometry. Estrogen metabolites were analyzed individually, in metabolic pathways (C-2, -4, or -16), and as ratios relative to parent estrogens. Geometric means of estrogen metabolites by tertiles of accelerometer-measures, adjusted for age and body mass, were computed using linear models.

RESULTS

High activity was associated with lower levels of estrone and estradiol (P trend = 0.01), whereas increased sedentary time was positively associated with these parent estrogens (P trend = 0.04). Inverse associations were observed between high activity and 2-methoxyestradiol, 4-methoxyestradiol, 17-epiestriol, and 16-epiestriol (P trend = 0.03). Sedentary time was positively associated with methylated catechols in the 2- and 4-hydroxylation pathways (P trend ≤ 0.04). Women in the highest tertile of activity had increased hydroxylation at the C-2, -4, and -16 sites relative to parent estrogens (P trend ≤ 0.02), whereas increased sedentary time was associated with a lower 16-pathway/parent estrogen ratio (P trend = 0.01).

CONCLUSIONS

Higher activity was associated with lower urinary estrogens, possibly through increased estrogen hydroxylation and subsequent metabolism, whereas sedentary behavior may reduce metabolism.

Soy Food Intake and Biomarkers of Breast Cancer Risk: Possible Difference in Asian Women?

Soy foods may protect against breast cancer in Asian but not in Western populations. We examined if the levels of various markers of breast cancer risk and inflammation, as well as the effects of soy food consumption on these markers, differ between Asian and non-Asian premenopausal women in two soy intervention trials. One study randomized 220 women to a 2-yr intervention and the other one randomized 96 women in a crossover design to examine the effects of consumption of 2 daily soy servings on nipple aspirate fluid (NAF) volume; estrogens in serum, NAF, and urine; insulin-like growth factor-1 (IGF-1), IGF-binding protein 3, and inflammatory markers in serum; and mammographic densities. Mixed linear models were applied to assess ethnic differences in biomarkers and response to the soy diet. Serum C-reactive protein, serum leptin, NAF volume, and NAF estrone sulfate were lower, while urinary isoflavones were higher in Asian than in non-Asian women. A significant interaction (p_interaction = 0.05) between ethnicity and soy diet was observed for IGF-1 but not for other biomarkers. The current findings suggest possible ethnic differences in levels of biomarkers for breast cancer risk but little evidence that Asian women respond differently to soy foods than non-Asian women.

Association of estrogen measurements in serum and urine of premenopausal women

AIMS

We evaluated conjugated and unconjugated urinary estrogen metabolites as surrogate biomarkers for serum levels of unconjugated E1 and E2 in premenopausal women.

MATERIALS & METHODS

Repeated blood and urine samples were analyzed for estrogens and their metabolites using radioimmunoassays and liquid chromatography/mass spectrometry.

RESULTS

The strongest correlation (r = 0.39) was observed between serum E1 and urinary E1 and E2. The correlations of urinary E2 (r = 0.35), E1 (r = 0.29), all E2 metabolites (r = 0.30), all E1 metabolites (r = 0.23) and total estrogens (r = 0.26) with serum E2 were only moderate although statistically significant. All correlations were substantially stronger for Whites than Asians.

CONCLUSION

Urinary E2 emerged as the best predictor for serum E1 and E2, but the large intra-subject variability in urinary estrogen levels limits its use as a biomarker.

Alcohol Consumption and Urinary Estrogens and Estrogen Metabolites in Premenopausal Women

In a cross-sectional analysis, we evaluated the associations of usual total alcohol and wine intake with a comprehensive profile of mid-luteal phase urinary estrogens and estrogen metabolites (referred to jointly as EM) in a sample of 603 premenopausal women participating in the Nurses' Health Study II (NHSII). A total of 15 individual EM (pmol/mg creatinine) were measured by a liquid chromatography/tandem mass spectrometry (LC-MS/MS) method with high accuracy and reproducibility. We used linear mixed models to calculate the adjusted geometric means of individual EM, EM grouped by metabolic pathways, and pathway ratios by category of alcohol intake with non-drinkers of alcohol as the referent. Total alcohol intake was not associated with total EM but was positively associated with estradiol (26% higher among women consuming >15 g/day vs. non-drinkers; P trend = 0.03). Wine consumption was positively associated with a number of EM measures including estradiol (22% higher among women consuming ≥ 5 drinks/week vs. non-drinkers, P trend < 0.0001). In conclusion, the total alcohol intake was positively and significantly associated with urinary estradiol levels. Some differences in urinary estrogen metabolites were observed with wine drinking, when compared with non-drinkers. This study strengthens the evidence that alcohol consumption might play a role in breast cancer and other estrogen-related conditions. Additional studies of premenopausal women are needed to further explore the association of alcohol, particularly the specific types of alcohol, on patterns of estrogen metabolism in blood, urine, and tissue.

Dietary Fat and Fiber Intakes Are Not Associated with Patterns of Urinary Estrogen Metabolites in Premenopausal Women

BACKGROUND

Interindividual differences in the bioavailability of potentially carcinogenic estrogen and estrogen metabolites (EMs) may play a role in the risk of breast cancer.

OBJECTIVE

We examined whether dietary intakes of fiber and fat influence premenopausal EM profiles through effects on estrogen synthesis, metabolism, or excretion.

METHODS

We conducted a cross-sectional analysis of 598 premenopausal women who participated in a reproducibility study (n = 109) or served as controls in a nested case-control study of breast cancer (n = 489) within the Nurses' Health Study II. Dietary intakes of fiber and fat were assessed via semiquantitative food frequency questionnaires in 1995 and 1999. Midluteal urine samples were collected between 1996 and 1999 and EMs were quantified with the use of HPLC-tandem mass spectrometry. Linear mixed models were used to estimate creatinine-adjusted geometric means for individual EMs and their pathway groups across categories of dietary intake while controlling for total energy intake and potential confounders.

RESULTS

Higher total dietary fiber intake (>25 g/d vs. ≤15 g/d) was associated with significantly higher concentrations of 4-methoxyestradiol (50% difference, P-difference = 0.01, P-trend = 0.004) and lower concentrations of 17-epiestriol (-27% difference, P-difference = 0.03, P-trend = 0.03), but was not associated with any other EMs. The associations did not vary by fiber intake from different sources. Total fat intake (>35% energy vs. ≤25% energy) was suggestively positively associated with 17-epiestriol (22.6% difference, P-difference = 0.14, P-trend = 0.06); the association was significant for polyunsaturated fatty acid (37% difference, P-difference = 0.01, P-trend = 0.01) and trans fat (36.1% difference, P-difference = 0.01, P-trend = 0.01) intakes.

CONCLUSION

Fiber and fat intakes were not strongly associated with patterns of estrogen metabolism in premenopausal women. Our data suggest estrogen metabolism is not a major mechanism through which dietary fiber and fat may affect breast or other hormone-related cancer risks.

Caffeine, coffee, and tea intake and urinary estrogens and estrogen metabolites in premenopausal women

BACKGROUND

Prior studies have found weak inverse associations between breast cancer and caffeine and coffee intake, possibly mediated through their effects on sex hormones.

METHODS

High-performance liquid chromatography/tandem mass spectrometry was used to quantify levels of 15 individual estrogens and estrogen metabolites (EM) among 587 premenopausal women in the Nurses' Health Study II with mid-luteal phase urine samples and caffeine, coffee, and/or tea intakes from self-reported food frequency questionnaires. Multivariate linear mixed models were used to estimate geometric means of individual EM, pathways, and ratios by intake categories, and P values for tests of linear trend.

RESULTS

Compared with women in the lowest quartile of caffeine consumption, those in the top quartile had higher urinary concentrations of 16α-hydroxyestrone (28% difference; Ptrend = 0.01) and 16-epiestriol (13% difference; Ptrend = 0.04), and a decreased parent estrogens/2-, 4-, 16-pathway ratio (Ptrend = 0.03). Coffee intake was associated with higher 2-catechols, including 2-hydroxyestradiol (57% difference, ≥4 cups/day vs. ≤6 cups/week; Ptrend = 0.001) and 2-hydroxyestrone (52% difference; Ptrend = 0.001), and several ratio measures. Decaffeinated coffee was not associated with 2-pathway metabolism, but women in the highest (vs. lowest) category of intake (≥2 cups/day vs. ≤1-3 cups/month) had significantly lower levels of two 16-pathway metabolites, estriol (25% difference; Ptrend = 0.01) and 17-epiestriol (48% difference; Ptrend = 0.0004). Tea intake was positively associated with 17-epiestriol (52% difference; Ptrend = 0.01).

CONCLUSION

Caffeine and coffee intake were both associated with profiles of estrogen metabolism in premenopausal women.

IMPACT

Consumption of caffeine and coffee may alter patterns of premenopausal estrogen metabolism.

Improved profiling of estrogen metabolites by orbitrap LC/MS

Estrogen metabolites are important biomarkers to evaluate cancer risks and metabolic diseases. Due to their low physiological levels, a sensitive and accurate method is required, especially for the quantitation of unconjugated forms of endogenous steroids and their metabolites in humans. Here, we evaluated various derivatives of estrogens for improved analysis by orbitrap LC/MS in human serum samples. A new chemical derivatization reagent was applied modifying phenolic steroids to form 1-methylimidazole-2-sulfonyl adducts. The method significantly improves the sensitivity 2-100 fold by full scan MS and targeted selected ion monitoring MS over other derivatization methods including, dansyl, picolinoyl, and pyridine-3-sulfonyl products.

Epidemiologic studies of estrogen metabolism and breast cancer

Early epidemiologic studies of estrogen metabolism measured only 2-hydroxyestrone and 16α-hydroxyestrone and relied on direct enzyme immunoassays without purification steps. Eight breast cancer studies have used these assays with prospectively collected blood or urine samples. Results were inconsistent, and generally not statistically significant; but the assays had limited specificity, especially at the low concentrations characteristic of postmenopausal women. To facilitate continued testing in population-based studies of the multiple laboratory-based hypotheses about the roles of estrogen metabolites, a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay was developed to measure concurrently all 15 estrogens and estrogen metabolites in human serum and urine, as unconjugated and total (glucuronidated+sulfated+unconjugated) concentrations. The assay has high sensitivity (lower limit of quantitation ∼1-2 pmol/L), reproducibility (coefficients of variation generally ⩽5%), and accuracy. Three prospective studies utilizing this comprehensive assay have demonstrated that enhanced 2-hydroxylation of parent estrogens (estrone+estradiol) is associated with reduced risk of postmenopausal breast cancer. In the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO) cohort, the serum ratio of 2-hydroxylation pathway metabolites to parent estrogens was associated with a 28% reduction in breast cancer risk across extreme deciles (p-trend=.05), after adjusting for unconjugated estradiol and breast cancer risk factors. Incorporating this ratio into a risk prediction model already including unconjugated estradiol improved absolute risk estimates substantially (by ⩾14%) in 36% of the women, an encouraging result that needs replication. Additional epidemiologic studies of the role of estrogen metabolism in the etiology of hormone-related diseases and continued improvement of estrogen metabolism assays are justified.

Assay reproducibility and interindividual variation for 15 serum estrogens and estrogen metabolites measured by liquid chromatography-tandem mass spectrometry

BACKGROUND

Interindividual differences in estrogen metabolism may partially account for differences in risks of estrogen-responsive cancers. We conducted a proof-of-performance study to assess the reproducibility of a LC/MS-MS method for measurement of 15 serum estrogens and metabolites (all 15 termed EM) in total (conjugated+unconjugated) and unconjugated forms and describe interindividual variation.

METHODS

Interindividual variation in serum EM profiles was evaluated for 20 premenopausal women, 15 postmenopausal women, and 10 men. Replicate aliquots from 10 premenopausal women, 5 postmenopausal women, and 5 men were assayed eight times over 4 weeks. Components of variance were used to calculate coefficients of variation (CV) and intraclass correlation coefficients (ICC).

RESULTS

In postmenopausal women and men, median EM concentrations were similar and substantially lower than that in premenopausal women. Within each sex/menopausal group, the sum of all EM varied 5- to 7-fold across extreme deciles. Some EM had greater variation; total estrone varied approximately 12-fold in premenopausal and postmenopausal women. Unconjugated estradiol varied 17-fold in postmenopausal women but only 5-fold in premenopausal women and men. CVs reflecting variation across replicate measures for individuals were <5% for most EM, but higher in some individuals with a low EM concentration. Overall laboratory CVs for all but one EM were <2% and ICCs were >99% for all EM in each group.

CONCLUSIONS

The serum EM assay has excellent laboratory reproducibility. In premenopausal women, postmenopausal women, and men, interindividual variation in EM measures is substantially greater than laboratory variation.

IMPACT

The serum EM assay is suitable for epidemiologic application. See all the articles in this CEBP Focus section, "Biomarkers, Biospecimens, and New Technologies in Molecular Epidemiology."

Oestrogen levels in serum and urine of premenopausal women eating low and high amounts of meat

OBJECTIVE

Based on the hypothesis that high-meat diets may increase breast cancer risk through hormonal pathways, the present analysis compared oestrogens in serum and urine by meat-eating status.

DESIGN

Intervention with repeated measures.

SETTING

Two randomized soya trials (BEAN1 and BEAN2) among premenopausal healthy women.

SUBJECTS

BEAN1 participants completed seven unannounced 24 h dietary recalls and donated five blood and urine samples over 2 years. BEAN2 women provided seven recalls and three samples over 13 months. Serum samples were analysed for oestrone (E₁) and oestradiol (E₂) using RIA. Nine oestrogen metabolites were measured in urine by LC-MS. Semi-vegetarians included women who reported consuming <30 g of red meat, poultry and fish daily, and pescatarians those who reported consuming <20 g of meat/poultry but >10 g of fish daily. All other women were classified as non-vegetarians. We applied mixed models to compute least-square means by vegetarian status adjusted for potential confounders.

RESULTS

The mean age of the 272 participants was 41·9 (SD 4·5) years. Serum E₁ (85 v. 100 pg/ml, P = 0·04) and E₂ (140 v. 154 pg/ml, P = 0·04) levels were lower in the thirty-seven semi-vegetarians than in the 235 non-vegetarians. The sum of the nine urinary oestrogen metabolites (183 v. 200 pmol/mg creatinine, P = 0·27) and the proportions of individual oestrogens and pathways did not differ by meat-eating status. Restricting the models to the samples collected during the luteal phase strengthened the associations.

CONCLUSIONS

Given the limitations of the study, the lower levels of serum oestrogens in semi-vegetarians than non-vegetarians need confirmation in larger populations.

Sources of variability in metabolite measurements from urinary samples

Background

The application of metabolomics in epidemiological studies would potentially allow researchers to identify biomarkers associated with exposures and diseases. However, within-individual variability of metabolite levels caused by temporal variation of metabolites, together with technical variability introduced by laboratory procedures, may reduce the study power to detect such associations. We assessed the sources of variability of metabolites from urine samples and the implications for designing epidemiologic studies.

Methods

We measured 539 metabolites in urine samples from the Navy Colon Adenoma Study using liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectroscopy (GC-MS). The study collected 2–3 samples per person from 17 male subjects (age 38–70) over 2–10 days. We estimated between-individual, within-individual, and technical variability and calculated expected study power with a specific focus on large case-control and nested case-control studies.

Results

Overall technical reliability was high (median intraclass correlation = 0.92), and for 72% of the metabolites, the majority of total variance can be attributed to between-individual variability. Age, gender and body mass index explained only a small proportion of the total metabolite variability. For a relative risk (comparing upper and lower quartiles of “usual” levels) of 1.5, we estimated that a study with 500, 1,000, and 5,000 individuals could detect 1.0%, 4.5% and 75% of the metabolite associations.

Conclusions

The use of metabolomics in urine samples from epidemiological studies would require large sample sizes to detect associations with moderate effect sizes.

Analgesic use and patterns of estrogen metabolism in premenopausal women

Analgesic use has been hypothesized to reduce the risk of some cancers, with inverse associations between analgesics and colon cancer, and suggestive inverse associations for breast cancer. Estrogen metabolites (EM) have genotoxic and estrogenic potential; genotoxicity may differ by hydroxylation pathway. Analgesic use may impact patterns of estrogen metabolism; effects of analgesics on disease risk could be mediated through these patterns. We conducted a cross-sectional study among 603 premenopausal women in the Nurses' Health Study II. Frequency of aspirin, non-aspirin nonsteroidal anti-inflammatory drugs (NSAIDs), and acetaminophen use was reported via questionnaire; average frequency in 1997 and 1999 was calculated. Women provided urine samples between 1996 and 1999, collected during the mid-luteal phase of the menstrual cycle. Urinary EM were quantified using high-performance liquid chromatography-tandem mass spectrometry. We observed no association between analgesic use and estradiol, estrone, or specific pathways of estrogen metabolism. Women reporting more frequent aspirin use had lower methylated 2-catechols (e.g., 2-hydroxyestrone-3-methyl ether, 2+ days/week vs. non-use: 0.95 vs. 1.21 pmol/mg creatinine; p difference = 0.01, p trend = 0.07). Non-aspirin NSAID use was positively associated with 17-epiestriol (4+ days/week vs. non-use: 2.48 vs. 1.52 pmol/mg creatinine; p difference = 0.01, p trend = 0.11). Acetaminophen use was positively associated with total EM (2+ days/week vs. non-use: 236 vs. 198 pmol/mg creatinine; p difference = 0.02, p trend = 0.11), 2-hydroxyestrone-3-methyl ether (1.6 vs. 1.1 pmol/mg creatinine; p difference < 0.01, p trend = 0.02), and 16α-hydroxyestrone (17 vs. 12 pmol/mg creatinine; p difference = 0.01, p trend = 0.05). This study provides the first assessment of analgesic use and patterns of estrogen metabolism in women. While we observed some associations between analgesics and individual EM, no clear patterns emerged.

Mass spectrometry techniques in the survey of steroid metabolites as potential disease biomarkers: a review

Mass spectrometric approaches have been fundamental to the identification of metabolites associated with steroid hormones, yet this topic has not been reviewed in depth in recent years. To this end, and given the increasing relevance of liquid chromatography-mass spectrometry (LC-MS) studies on steroid hormones and their metabolites, the present review addresses this subject. This review provides a timely summary of the use of various mass spectrometry-based analytical techniques during the evaluation of steroidal biomarkers in a range of human disease settings. The sensitivity and specificity of these technologies are clearly providing valuable new insights into breast cancer and cardiovascular disease. We aim to contribute to an enhanced understanding of steroid metabolism and how it can be profiled by LC-MS techniques.

Urinary estrogen metabolites and breast cancer: a combined analysis of individual level data

BACKGROUND

Circulating estrogens are associated with increased breast cancer risk, yet the role of estrogen metabolites in breast carcinogenesis remains unclear. This combined analysis of 5 published studies evaluates urinary 2-hydroxyestrone (2-OHE1), 16α-hydroxyestrone (16α-OHE1), and their ratio (2:16α-OHE1) in relation to breast cancer risk.

METHODS

Primary data on 726 premenopausal women (183 invasive breast cancer cases and 543 controls) and 1,108 postmenopausal women (385 invasive breast cancer cases and 723 controls) were analyzed. Urinary estrogen metabolites were measured using enzyme linked immunosorbent assays. Study-specific and combined multivariable adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were estimated based on tertiles of estrogen metabolites. Multinomial logistic regression models were fit according to hormone receptor status.


RESULTS

Higher premenopausal 2:16α-OHE1 was suggestive of reduced breast cancer risk overall (study-adjusted ORIIIvsI=0.80; 95% CI: 0.49-1.32) and for estrogen receptor negative (ER-) subtype (ORIIIvsI=0.33; 95% CI: 0.13-0.84). Among postmenopausal women, 2:16α-OHE1 was unrelated to breast cancer risk (study-adjusted ORIIIvsI=0.93; 95% CI: 0.65-1.33); however, the association between 2-OHE1 and risk varied by body mass index (p-interaction=0.003).

CONCLUSIONS

Premenopausal urinary 2:16α-OHE1 may play a role in breast carcinogenesis; however, larger studies are needed. Our findings do not support reduced breast cancer risk with higher postmenopausal 2:16α-OHE1 overall, although obesity may modify associations with 2-OHE1.

Green tea intake is associated with urinary estrogen profiles in Japanese-American women

Scope

Intake of green tea may reduce the risk of breast cancer; polyphenols in this drink can influence enzymes that metabolize estrogens, known causal factors in breast cancer etiology.

Methods and results

We examined the associations of green tea intake (<1 time/week, 1-6 times weekly, or 7+ times weekly) with urinary estrogens and estrogen metabolites (jointly EM) in a cross-sectional sample of healthy Japanese American women, including 119 premenopausal women in luteal phase and 72 postmenopausal women. We fit robust regression models to each log-transformed EM concentration (picomoles per mg creatinine), adjusting for age and study center. In premenopausal women, intake of green tea was associated with lower luteal total EM (P trend = 0.01) and lower urinary 16-pathway EM (P trend = 0.01). In postmenopausal women, urinary estrone and estradiol were approximately 20% and 40% lower (P trend = 0.01 and 0.05, respectively) in women drinking green tea daily compared to those drinking <1 time/week. Adjustment for potential confounders (age at menarche, parity/age at first birth, body mass index, Asian birthplace, soy) did not change these associations.

Conclusions

Findings suggest that intake of green tea may modify estrogen metabolism or conjugation and in this way may influence breast cancer risk.

Urinary concentrations of estrogens and estrogen metabolites and smoking in caucasian women

BACKGROUND

Smoking has been hypothesized to decrease biosynthesis of parent estrogens (estradiol and estrone) and increase their metabolism by 2-hydroxylation. However, comprehensive studies of smoking and estrogen metabolism by 2-, 4-, or 16-hydroxylation are sparse.

METHODS

Fifteen urinary estrogens and estrogen metabolites (jointly called EM) were measured by liquid chromatography/tandem mass spectrometry (LC/MS-MS) in luteal phase urine samples collected during 1996 to 1999 from 603 premenopausal women in the Nurses' Health Study II (NHSII; 35 current, 140 former, and 428 never smokers). We calculated geometric means and percentage differences of individual EM (pmol/mg creatinine), metabolic pathway groups, and pathway ratios, by smoking status and cigarettes per day (CPD).

RESULTS

Total EM and parent estrogens were nonsignificantly lower in current compared with never smokers, with estradiol significant (P(multivariate) = 0.02). We observed nonsignificantly lower 16-pathway EM (P = 0.08) and higher 4-pathway EM (P = 0.25) and similar 2-pathway EM in current versus never smokers. EM measures among former smokers were similar to never smokers. Increasing CPD was significantly associated with lower 16-pathway EM (P-trend = 0.04) and higher 4-pathway EM (P-trend = 0.05). Increasing CPD was significantly positively associated with the ratios of 2- and 4-pathway to parent estrogens (P-trend = 0.01 and 0.002), 2- and 4-pathway to 16-pathway (P-trend = 0.02 and 0.003), and catechols to methylated catechols (P-trend = 0.02).

CONCLUSIONS

As hypothesized, we observed lower urinary levels of total EM and parent estrogens in active smokers. Our results also suggest smoking is associated with altered estrogen metabolism, specifically increased 2- and 4-hydroxylation, decreased 16-hydroxylation, and decreased catechol methylation.

IMPACT

Our study suggests how smoking might influence estrogen-related cancers and conditions.

Body size in relation to urinary estrogens and estrogen metabolites (EM) among premenopausal women during the luteal phase

Estrogen metabolism profiles may play an important role in the relationship between body size and breast carcinogenesis. Previously, we observed inverse associations between current body mass index (BMI) and plasma levels of parent estrogens (estrone and estradiol) among premenopausal women during both follicular and luteal phases. Using data from the Nurses' Health Study II, we assessed whether height, current BMI, and BMI at age 18 were associated with the urinary concentrations of 15 estrogens and estrogen metabolites (jointly referred to as EM) measured during the luteal phase among 603 premenopausal women. We observed inverse associations with total EM for height (P (trend) = 0.01) and current BMI (P (trend) = 0.01), but not BMI at age 18 (P (trend) = 0.26). Six EMs were 18-27% lower in women with a height 68+ versus ≤62 in., primarily in the methylated catechol pathway (P (trend) = 0.04). Eight EMs were 18-50% lower in women with a BMI of 30+ versus <20, primarily in the 2-catechol and methylated catechol pathways (P (trend) < 0.001 for both). Our results suggest that height and current BMI are associated with estrogen metabolism profiles in premenopausal women. Further studies with timed urine and blood collections are required to confirm and extend our findings.

Urinary estrogens and estrogen metabolites and mammographic density in premenopausal women

Mammographic density is a strong and independent risk factor for breast cancer and is considered an intermediate marker of risk. The major predictors of premenopausal mammographic density, however, have yet to be fully elucidated. To test the hypothesis that urinary estrogen metabolism profiles are associated with mammographic density, we conducted a cross-sectional study among 352 premenopausal women in the Nurses' Health Study II (NHSII). We measured average percent mammographic density using a computer-assisted method. In addition, we assayed 15 estrogens and estrogen metabolites (jointly termed EM) in luteal-phase urine samples. We used multivariable linear regression to quantify the association of average percent density with quartiles of each individual EM as well as the sum of all EM (total EM), EM groups defined by metabolic pathway, and pathway ratios. In multivariable models controlling for body mass index and other predictors of breast density, women in the top quartile of total EM had an average percent density 3.4 percentage points higher than women in the bottom quartile (95 % confidence interval: -1.1, 8.0; p trend = 0.08). A non-significant positive association was noted for the 2-hydroxylation pathway catechols (breast density was 4.0 percentage points higher in top vs. bottom quartile; p trend = 0.06). In general, we observed no associations with parent estrogens or the 4- or 16-hydroxylation pathways or pathway ratios. These results suggest that urinary luteal estrogen profiles are not strongly associated with premenopausal mammographic density. If these profiles are associated with breast cancer risk, they may not act through influences on breast density.

Association between physical activity and urinary estrogens and estrogen metabolites in premenopausal women

OBJECTIVE

The objective of the study was to evaluate in premenopausal women the relationships of physically active and sedentary behaviors reported for adulthood and adolescence with a comprehensive profile of estrogen metabolism.

METHODOLOGY

Fifteen estrogens and estrogen metabolites (jointly termed EM) were measured using liquid chromatography-tandem mass spectrometry in luteal phase urines from 603 premenopausal women in the Nurses' Health Study II. Geometric means of individual EM, metabolic pathway groups, and pathway ratios were examined by level of exposure after adjustment for age, body mass index, alcohol intake, menstrual cycle length, and sample collection timing.

RESULTS

High overall physical activity in adulthood (42+ metabolic equivalent h/wk vs. <3 metabolic equivalent h/wk) was associated with a 15% lower level of urinary estradiol (Ptrend=0.03) and 15% lower level of 16-hydroxylation pathway EM (Ptrend=0.03). Levels of 2- and 4-hydroxylation pathway EM did not differ significantly by physical activity. High overall activity was also positively associated with four ratios: 2-pathway EM to parent estrogens (Ptrend=0.05), 2-pathway catechols to parent estrogens (Ptrend=0.03), 2-pathway catechols to methylated 2-pathway catechols (Ptrend<0.01), and 2-hydroxyestrone to 16α-hydroxyestrone (Ptrend=0.01). Similar patterns of association were noted for walking and vigorous physical activity, but there was little evidence of associations with sedentary behaviors or activity during adolescence.

CONCLUSIONS

High levels of physical activity were associated with lower levels of parent estrogens and 16-hydroxylation pathway EM and preferential metabolism to 2-pathway catechols. The results of our analysis, the largest, most comprehensive examination of physical activity and estrogen metabolism to date, may be useful in future studies investigating the etiology of diseases linked to both physical activity and endogenous estrogen.

Urinary estrogen metabolites in two soy trials with premenopausal women

Background

Soy consumption may protect against breast cancer through modification of estrogen metabolism.

Objective

We examined the effect of soy foods on urinary estrogens and the 2-hydroxy (OH)/16α-OH estrone (E₁) ratio in 2 dietary interventions with premenopausal women.

Methods

BEAN1 was a 2-year randomized trial and BEAN2 a 13-month randomized crossover study. In both interventions, study participants consumed a high-soy diet with 2 soy food servings/day and a low-soy diet with <3 servings of soy/week. Urine samples were collected at baseline and at the end of the diet periods, analyzed for 9 estrogen metabolites by liquid chromatography mass spectrometry, and adjusted for creatinine levels. For BEAN1, 2 samples for 188 participants and for BEAN2, 3 samples for 79 women were analyzed. We applied mixed-effects regression models with log-transformed values of estrogen metabolites and soy intake as the exposure variable.

Results

In BEAN1, no effect of the high-soy diet on individual estrogen metabolites or hydroxylation pathways was observed. The median 2-OH/16α-OH E₁ ratio decreased non-significantly in the intervention group from 6.2 to 5.2 as compared to 6.8 and 7.2 in the control group (p=0.63). In BEAN2, only 4-OHE₁ was significantly lower after the high-soy diet. Interaction terms of the high-soy diet with equol producer status, ethnicity, and weight status revealed no significant effect modification.

Conclusions

Contrary to our hypothesis and some previous reports, the results from 2 well controlled dietary interventions do not support an effect of a high-soy diet on a panel of urinary estrogen metabolites and the 2-OH/16α-OHE₁ ratio.

Association between reproductive factors and urinary estrogens and estrogen metabolites in premenopausal women

BACKGROUND

Little is known about relationships among reproductive factors, estrogens and estrogen metabolites (jointly referred to as EM), and estrogen metabolism patterns.

METHODS

In a cross-sectional analysis, we examined the associations of age at menarche, menstrual cycle length and regularity, parity, age at first and last birth, breastfeeding, and duration of and time since use of oral contraceptives with mid-luteal phase urinary EM in a sample of 603 premenopausal women, ages 33 to 51 years, within the Nurses' Health Study II (NHSII). Fifteen individual urinary EMs were measured with liquid chromatography/tandem mass spectrometry (LC/MS-MS) and analyzed both individually and in metabolic pathways.

RESULTS

Compared with women with extremely regular cycles, those with irregular cycles had lower levels of total EM (percent difference = 24%; P(trend) = 0.01), estradiol (23%; P(trend) = 0.02), and 16-hydroxylation pathway EM (32%; P(trend) < 0.01). Longer menstrual cycles were associated with higher levels of estrone (percent difference ≥32 vs. <26 days: 25%; P(trend) = 0.03), estradiol (24%; P(trend) = 0.01), and 16-hydroxylation pathway EM (22%; P(trend) = 0.02). Among parous women, older age at first birth was associated with lower 16-hydroxylation pathway EM (percent difference age at first birth >35 vs. ≤25 years: 20%; P(trend) = 0.02). The other reproductive factors were not statistically significantly associated with individual urinary EM or EM pathways.

CONCLUSIONS AND IMPACT

These data, based on a LC/MS-MS assay with high specificity and precision, provide an initial, comprehensive evaluation of the associations between reproductive factors and estrogen metabolism patterns.

The relation of urinary estrogen metabolites with mammographic densities in premenopausal women

BACKGROUND

Mammographic density is a strong predictor of breast cancer risk. The total amount and the metabolism of endogenous estrogens, e.g., the ratio of 2-hydroxyestrone (2-OHE(1)) and 16α-OHE(1) may influence breast cancer risk. This study examined the association of urinary estrogen metabolites with breast density in premenopausal women.

METHODS

Urine samples were collected at baseline and after 2 years, analyzed for 11 estrogen metabolites plus progesterone and testosterone by liquid chromatography mass spectrometry, and adjusted for creatinine levels. Mixed-effects regression was applied to examine the association of estrogens with breast density.

RESULTS

Total estrogen metabolites (181 ± 113 vs. 247 ± 165 pmol/mg creatinine, p=0.01) and the 2/16α-OH ratio (8.4 ± 10.4 vs. 13.0 ± 17.1, p=0.02) were lower in the 74 Asian than in the 114 non-Asian women. In adjusted models, positive associations of total estrogen metabolites (p=0.002) and the 2/16α-OHE(1) ratio (p=0.08) with percent density were detected in Asians only. In all women, mammographic density was positively associated with the 2-OH pathway (p=0.01), inversely related to the 16α-OH pathway (p=0.01), and not associated with the 4-OH pathway, testosterone, and progesterone. Results for the size of the dense area weakly reflected the findings for percent density, while associations with the non-dense area were in the opposite direction.

CONCLUSIONS

The findings that the 2-OH pathway is associated with higher and the 16α-OH pathway with lower breast density contradicts the hypothesized risk profile of these metabolites, but, if a relation between estrogen metabolites and breast cancer risk exists, it may be mediated through pathways other than mammographic density.

Urinary estrogens and estrogen metabolites and subsequent risk of breast cancer among premenopausal women

Endogenous estrogens and estrogen metabolism are hypothesized to be associated with premenopausal breast cancer risk but evidence is limited. We examined 15 urinary estrogens/estrogen metabolites and breast cancer risk among premenopausal women in a case-control study nested within the Nurses' Health Study II (NHSII). From 1996 to 1999, urine was collected from 18,521 women during the mid-luteal menstrual phase. Breast cancer cases (N = 247) diagnosed between collection and June 2005 were matched to two controls each (N = 485). Urinary estrogen metabolites were measured by liquid chromatography-tandem mass spectrometry and adjusted for creatinine level. Relative risks (RR) and 95% confidence intervals (CI) were estimated by multivariate conditional logistic regression. Higher urinary estrone and estradiol levels were strongly significantly associated with lower risk (top vs. bottom quartile RR: estrone = 0.52; 95% CI, 0.30-0.88; estradiol = 0.51; 95% CI, 0.30-0.86). Generally inverse, although nonsignificant, patterns also were observed with 2- and 4-hydroxylation pathway estrogen metabolites. Inverse associations generally were not observed with 16-pathway estrogen metabolites and a significant positive association was observed with 17-epiestriol (top vs. bottom quartile RR = 1.74; 95% CI, 1.08-2.81; P(trend) = 0.01). In addition, there was a significant increased risk with higher 16-pathway/parent estrogen metabolite ratio (comparable RR = 1.61; 95% CI, 0.99-2.62; P(trend) = 0.04). Other pathway ratios were not significantly associated with risk except parent estrogen metabolites/non-parent estrogen metabolites (comparable RR = 0.58; 95% CI, 0.35-0.96; P(trend) = 0.03). These data suggest that most mid-luteal urinary estrogen metabolite concentrations are not positively associated with breast cancer risk among premenopausal women. The inverse associations with parent estrogen metabolites and the parent estrogen metabolite/non-parent estrogen metabolite ratio suggest that women with higher urinary excretion of parent estrogens are at lower risk.

The effect of tamoxifen and raloxifene on estrogen metabolism and endometrial cancer risk

Selective estrogen receptor modulators (SERMs) demonstrate differential endometrial cancer (EC) risk. While tamoxifen (TAM) use increases the risk of endometrial hyperplasia and malignancy, raloxifene (RAL) has neutral effects on the uterus. How TAM increases the risk of EC and why TAM and RAL differentially modulate the risk for EC, however, remain elusive. Here, we tested the hypothesis that TAM increases the risk for EC, at least in part, by enhancing the local estrogen biosynthesis and directing estrogen metabolism towards the formation of genotoxic and hormonally active estrogen metabolites. In addition, the differential effects of TAM and RAL in EC risk are attributed to their differential effect on estrogen metabolism/metabolites. The endometrial cancer cell line (Ishikawa cells) and the nonmalignant immortalized human endometrial glandular cell line (EM1) were used for the study. The profile of estrogen/estrogen metabolites (EM), depurinating estrogen-DNA adducts, and the expression of estrogen-metabolizing enzymes in cells treated with 17β-estradiol (E2) alone or in combination with TAM or RAL were investigated using high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS(2)), ultraperformance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS), and Western blot analysis, respectively. TAM significantly increased the total EM and enhanced the formation of hormonally active and carcinogenic estrogen metabolites, 4-hydroxestrone (4-OHE1) and 16α-hydroxyestrone, with concomitant reduction in the formation of antiestrogenic and anticarcinogenic 2-hydroxyestradiol and 2-methoxyestradiol. Furthermore, TAM increased the formation of depurinating estrogen-DNA adducts 4-OHE1 [2]-1-N7Guanine and 4-OHE1 [2]-1-N3 Adenine. TAM-induced alteration in EM and depurinating DNA adduct formation is associated with altered expression of estrogen metabolizing enzymes CYP1A1, CYP1B1, COMT, NQO1, and SF-1 as revealed by Western blot analysis. In contrast to TAM, RAL has minimal effect on EM, estrogen-DNA adduct formation, or estrogen-metabolizing enzymes expression. These data show that TAM perturbs the balance of estrogen-metabolizing enzymes and alters the disposition of estrogen metabolites, which can explain, at least in part, the mechanism for TAM-induced EC. These results also implicate the differential effect of TAM and RAL on estrogen metabolism/metabolites as a potential mechanism for their disparate effects on the endometrium.

Analysis of urinary estrogens, their oxidized metabolites, and other endogenous steroids by benchtop orbitrap LCMS versus traditional quadrupole GCMS

Estrogens and other endogenous steroids are known risk markers for cancer. Gas chromatography (GC) with mass spectrometry (MS) has traditionally predominated the analysis of estrogens and other endogenous steroids, but liquid chromatography (LC) MS is increasingly favored. Direct comparisons of the two technologies have hitherto not been performed. Steroids were analyzed from 232 urine samples of 78 premenopausal women in a blinded fashion by benchtop orbitrap LCMS and single quadrupole GCMS. Sixteen steroidal estrogens including oxidized metabolites could be analyzed by LCMS. LCMS-GCMS Spearman rank correlations of the major estrogens E(1), E(2), E(3), 16α-OHE(1), and 2-OHE(1) were very high (r = 0.72-0.91), and absolute concentrations also agreed (<5% difference for E(1), E(2), E(3), 16α-OHE(1)). LCMS allowed reinterrogation of the acquired data due to orbitrap technology, which permitted post-analysis quantitation of progesterone, cortisol, and cortisone (LCMS-GCMS Spearman rank correlations = 0.80-0.84; absolute difference, <7%; n = 137). GCMS allows the measurement of a wide range of steroids including non-polar analytes that escape the presented LCMS assay. In contrast, orbitrap-based LCMS can detect more estrogens, is faster, less costly, allows post-data acquisition reinterrogation of certain analytes that had not been targeted a priori, and requires much less urine.

A new approach to measuring estrogen exposure and metabolism in epidemiologic studies

Endogenous estrogen plays an integral role in the etiology of breast and endometrial cancer, and conceivably ovarian cancer. However, the underlying mechanisms and the importance of patterns of estrogen metabolism and specific estrogen metabolites have not been adequately explored. Long-standing hypotheses, derived from laboratory experiments, have not been tested in epidemiologic research because of the lack of robust, rapid, accurate measurement techniques appropriate for large-scale studies. We have developed a stable isotope dilution liquid chromatography-tandem mass spectrometry (LC-MS(2)) method that can measure concurrently all 15 estrogens and estrogen metabolites (EM) in urine and serum with high sensitivity (level of detection=2.5-3.0fmol EM/mL serum), specificity, accuracy, and precision [laboratory coefficients of variation (CV's) < or =5% for nearly all EM]. The assay requires only extraction, a single chemical derivatization, and less than 0.5mL of serum or urine. By incorporating enzymatic hydrolysis, the assay measures total (glucuronidated+sulfated+unconjugated) EM. If the hydrolysis step is omitted, the assay measures unconjugated EM. Interindividual differences in urinary EM concentrations (pg/mL creatinine), which reflect total EM production, were consistently large, with a range of 10-100-fold for nearly all EM in premenopausal and postmenopausal women and men. Correlational analyses indicated that urinary estrone and estradiol, the most commonly measured EM, do not accurately represent levels of total urinary EM or of the other EM. In serum, all 15 EM were detected as conjugates, but only 5 were detected in unconjugated form. When we compared our assay methods with indirect radioimmunoassays for estrone, estradiol, and estriol and enzyme-linked immunosorbent assays for 2-hydroxyestrone and 16alpha-hydroxyestrone, ranking of individuals agreed well for premenopausal women [Spearman r (r(s))=0.8-0.9], but only moderately for postmenopausal women (r(s)=0.4-0.8). Our absolute readings were consistently lower, especially at the low concentrations characteristic of postmenopausal women, possibly because of improved specificity. We are currently applying our EM measurement techniques in several epidemiologic studies of premenopausal and postmenopausal breast cancer.

Reproducibility of plasma and urine biomarkers among premenopausal and postmenopausal women from the Nurses' Health Studies

BACKGROUND

Temporal variability of biomarkers should be evaluated before their use in epidemiologic studies.

METHODS

We evaluated the reproducibility, using intraclass correlation coefficients (ICC), of 77 plasma and 9 urinary biomarkers over 1 to 3 years among premenopausal (n = 40) and postmenopausal (n = 35-70) participants from the Nurses' Health Study and Nurses' Health Study II.

RESULTS

Plasma and urinary stress hormones and melatonin were measured among premenopausal women, whereas melatonin and the remaining biomarkers were measured in postmenopausal women. ICCs were good to excellent for plasma carotenoids (0.73-0.88), vitamin D analytes (0.56-0.72), bioactive somatolactogens (0.62), soluble leptin receptor (0.82), resistin (0.74), and postmenopausal melatonin (0.63). Reproducibility was lower for some of the plasma fatty acids (0.38-0.72), matrix metalloproteinases (0.07-0.91), and premenopausal melatonin (0.44). The ICCs for plasma and urinary phytoestrogens were poor (< or = 0.09) except for enterolactone (plasma, 0.44; urinary, 0.52). ICCs for the stress hormones among premenopausal women ranged from 0 (plasma cortisol) to 0.45 (urinary dopamine).

CONCLUSIONS

Our results indicate that for the majority of these markers, a single measurement can reliably estimate average levels over a 1- to 3-year period in epidemiologic studies. For analytes with fair to good ICCs, reproducibility data can be used for measurement error correction. Analytes with poor ICCs should only be used in settings with multiple samples per subject or in populations in which ICCs are higher.

IMPACT

This article summarizes the feasibility of the use of >80 biomarkers in epidemiologic studies in which only one biospecimen is available to represent longer term exposure.

Circulating sex steroids and breast cancer risk in premenopausal women

Evidence from both laboratory and epidemiologic studies indicate a key role of hormones in the etiology of breast cancer. In epidemiologic studies, indirect data, including the consistent associations observed between reproductive factors and breast cancer risk, support an important contribution of hormones to risk. Recently, the associations between circulating hormones in premenopausal women and subsequent risk of breast cancer have been evaluated. To date, both positive and null associations have been observed for estrogens and inverse and null associations for progesterone with breast cancer risk. For estrogens, the relationships may vary by menstrual cycle phase (e.g., follicular versus luteal phase), although this requires confirmation. Few studies have evaluated estrogen metabolites in relation to breast cancer risk; hence, no conclusions can yet be drawn. Findings for the largely adrenal-derived dehydroepiandrosterone (DHEA) and DHEA sulfate also are inconsistent and may vary by age. However, relatively consistent positive associations have been observed between testosterone (or free testosterone) levels and breast cancer risk; these associations are of similar magnitude to those confirmed among postmenopausal women. In this review, we summarize current evidence and identify gaps and inconsistencies that need to be addressed in future studies of sex steroids and premenopausal breast cancer risk.