Interplay Between Insulin Resistance and Estrogen Deficiency as co- Activators in Carcinogenesis

Both insulin resistance and estrogen deficiency result in complex metabolic disorder based mainly on defective cellular glucose uptake and on an atherogenic serum lipid profile. These alterations may be regarded as high risks for several life-threatening human diseases, such as type-2 diabetes, cardiovascular lesions and malignancies. Insulin resistance and estrogen deficiency are concomitant disorders with mutual interrelationship. Insulin resistance and the compensatory hyperinsulinemia provoke increased androgen synthesis at the expense of decreased estrogen production. Similarly, a moderate or severe decrease in serum estrogen levels enhances the prevalence of insulin resistant states both in men and women. Healthy premenopausal women enjoy the defensive effect of estrogens against metabolic and hormonal disorders. However, even a slight decrease in their circulatory estrogen levels associated with insulin resistance may increase the risk for cancers, particularly in the organs having high estrogen demand (breast, endometrium and ovary). On the other hand, postmenopausal state with profound estrogen deficiency confers high risk for cancers in different organs with either high or moderate estrogen demand. After menopause, hormone replacement therapy improves insulin sensitivity and decreases the enhanced inclination to malignancies in postmenopausal women. Recognition of the thorough interplay between insulin resistance and estrogen deficiency may illuminate many apparently controversial experimental and clinical findings concerning cancer development and therapeutic possibilities. Moreover, their interactions in the initiation and progression of human malignancies may supply new strategies in primary cancer prevention and cancer cure.     

Inhibition of progesterone-induced VEGF production in human breast cancer cells by the pure antiestrogen ICI 182,780

Initiation and/or promotion of endometrial cancer is known to be associated with estrogen and androgen (androstenedione) excess as well as with hyperinsulinemia/insulin resistance. It is possible that some allelic polymorphisms of the genes involved in steroidogenesis or steroid metabolism contribute to endometrial cancer susceptibility. We evaluated here the role of CYP17 biallelic (MspAI) polymorphism in 114 endometrial cancer patients compared with 182 healthy women. Our data demonstrated that A2/A2 CYP17 genotype, considered on the basis of initial breast cancer studies as 'unfavorable', was under-represented in endometrial cancer group (odds ratio 0.48, 95% confidence interval 0.25-0.89) that confirmed results of two other recent investigations. Carriers of this genotype were characterized by having lower blood insulin (by 120 min of oral glucose tolerance test 36.7+/-3.9 microU/ml vs. 90.4+/-16.7 microU/ml in postmenopausal women with A1/A1 genotype, P=0.04) and C-peptide levels (after night fasting 575.2+/-78.3 pg/ml vs. 978.9+/-115.7 pg/ml, respectively, P=0.04). No significant difference was found between the mean concentrations of testosterone, dehydroepiandrosterone sulfate and estradiol concentrations in patients-carriers of separate CYP17 genotypes. Thus, CYP17 polymorphism (namely, carrying the 'normal' A1/A1 genotype) might be one of the risk factors for endometrial cancer development. A1/A1 CYP17 variant may be associated with untraditional (non-steroidal) pathways that calls for corresponding preventive measures in high-risk groups.     

Nutrition, hormones, and breast cancer: Is insulin the missing link?

Breast cancer incidence rates are high in societies with a Western lifestyle characterized by low levels of physical activity, and by an energy-dense diet rich in total and saturated fat and refined carbohydrates. Epidemiologic studies, so far mostly on postmenopausal women, have shown that breast cancer risk is increased in hyperandrogenic women, with decreased levels of plasma sex-hormone binding globulin, and with increased levels of testosterone and of free estrogens. This paper describes the role of hyperinsulinemia as a physiologic link between nutritional lifestyle factors, obesity, and the development of a hyperandrogenic endocrine profile, and reviews evidence that may or may not support the theory that chronic hyperinsulinemia is an underlying cause of breast cancer. An hypothesis is presented, stipulating that breast cancer risk is increased not only in hyperandrogenic postmenopausal women, but also in premenopausal women with mild hyperandrogenism and normal (ovulatory) menstrual cycles. The author suggests further investigation as to whether there is a positive association between risk of breast cancer before menopause and subclinical forms of the polycystic ovary syndrome (PCOS), and to what extent diet and physical activity during childhood, by modulating the degree of insulin resistance during adolescence, may or may not be determinants of a PCO-like hyperandrogenic endocrine profile persisting into adulthood.Dr Kaaks is with the International Agency for Research on Cancer, Lyon, France. Address correspondence to Dr Kaaks, International Agency for Research on Cancer, 150 cours Albert-Thomas, 69372 Lyon Cedex 08, France.     

Serum C-peptide levels and breast cancer risk: results from the European Prospective Investigation into Cancer and Nutrition (EPIC)

It has been hypothesized that chronic hyperinsulinemia, a major metabolic consequence of physical inactivity and excess weight, might increase breast cancer risk by direct effects on breast tissue or indirectly by increasing bioavailable levels of testosterone and estradiol. Within the European Prospective Investigation into Cancer and Nutrition (EPIC), we measured serum levels of C-peptide--a marker for pancreatic insulin secretion--in a total of 1,141 incident cases of breast cancer and 2,204 matched control subjects. Additional measurements were made of serum sex hormone binding globulin (SHBG) and sex steroids. Conditional logistic regression models were used to estimate breast cancer risk for different levels of C-peptide. C-peptide was inversely correlated with SHBG and hence directly correlated with free testosterone among both pre and postmenopausal women. C-peptide and free estradiol also correlated positively, but only among postmenopausal women. Elevated serum C-peptide levels were associated with a nonsignificant reduced risk of breast cancer diagnosed up to the age of 50 years [odds ratio (OR)=0.70, (95% confidence interval (CI), 0.39-1.24); ptrend=0.05]. By contrast, higher levels of C-peptide were associated with an increase of breast cancer risk among women above 60 years of age, however only among those women who had provided a blood sample under nonfasting conditions [OR=2.03, (95% CI, 1.20-3.43); ptrend=0.01]. Our results do not support the hypothesis that chronic hyperinsulinemia generally increases breast cancer risk, independently of age. Nevertheless, among older, postmenopausal women, hyperinsulinemia might contribute to increasing breast cancer risk.     

Energetic factors, ovarian steroids and the risk of breast cancer.

In industrial countries, women often have excess metabolic energy due to high food consumption and low physical activity. High lifetime energy availability results in high lifetime levels of ovarian steroid hormones. Oestrogens and progesterone are hypothesized to play a crucial role in the development and prognosis of breast cancer. Epidemiological studies document the importance of physical activity and caloric limitations in reducing breast cancer risk. The risk of breast cancer is much higher in industrial countries than in developing countries, where women are characterized by lower energy intake and higher energy expenditure. It is likely, that the beneficial effects of physical activity and of negative energy balance are mediated by the reduced levels of ovarian steroids. While both weight loss and physical activity may have similar efficacy in suppressing ovarian function and, therefore, in reducing the risk of breast cancer, we suggest that it may be more advantageous for premenstrual women to achieve lifetime reduction in steroid levels by increasing their physical activity, rather than by weight loss due to caloric restriction alone.     

Ovarian volume: determinants and associations with cancer among postmenopausal women.

Clinical studies have reported associations between ovarian stromal hyperplasia and the diagnosis of hormonally related tumors such as endometrial cancer. To assess the hypothesis that characteristics of benign ovaries among postmenopausal women are related to risk for breast, endometrial, and colon cancer, we analyzed systematically collected transvaginal ultrasound data for participants enrolled in the screening arm of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. Among women without cancer, median ovarian volume declined with age from 1.25 cm3 for women between ages 55 and 59 years to 1.0 cm3 for those between ages 65 and 69 years. African American and Caucasian women had larger median ovarian volumes than Asians. Larger ovarian volume was also associated with the highest quartiles of height and weight and ever having smoked. After adjusting for race, age, parity, body mass, smoking, and hormone use, women with median ovarian volumes >or=3.0 cm3 were at increased risk for breast cancer [odds ratio (OR), 1.42; 95% confidence interval (95% CI), 1.11-1.70], endometrial cancer (OR, 1.97; 95% CI, 1.12-3.48), and colon cancer (OR, 2.00; 95% CI, 1.25-3.21). Significant trends of risk with increasing volume were found only for breast and endometrial cancers. We conclude that large ovaries among postmenopausal women may represent a marker of risk for hormonally related tumors. Confirmation of these findings in future studies, including analyses of serum hormone levels and tissues, may provide insights into hormonal carcinogenesis among older women.     

Loss of cables, a cyclin-dependent kinase regulatory protein, is associated with the development of endometrial hyperplasia and endometrial cancer

Endometrial cancer is the most common gynecological cancer in Western industrialized countries. Cables, a cyclin-dependent kinase binding protein, plays a role in proliferation and/or differentiation. Cables mutant mice are viable, but develop endometrial hyperplasia and carcinoma in situ at a young age. Exposure to chronic low levels of estrogen results in development of endometrial cancer, similar to that observed in the postmenopausal female. In vitro and in vivo studies demonstrate that levels of Cables mRNA in benign human endometrial epithelium are up-regulated by progesterone and down-regulated by estrogen. Furthermore, nuclear immunostaining for Cables is lost in a high percentage of cases of human endometrial hyperplasia and adenocarcinoma, which are likely the product of unopposed estrogen. The loss of Cables immunostaining in the human endometrial cancer samples correlates with a marked decrease in Cables mRNA. Ectopic expression of Cables in human endometrial cells dramatically slows cell proliferation. Collectively, these data provide evidence that Cables is hormonally regulated and is involved in regulating endometrial cell proliferation. In addition, loss or suppression of Cables may be an early step in the development of endometrial cancer.     

Risk of endometrial cancer following cessation of menopausal hormone use (Washington, United States)

While there are a number of benefits to the health of postmenopausal women from use of unopposed estrogens, the increased risk of endometrial cancer related to these hormones has led many women to use combined estrogen-progestogen therapy instead, or not to use hormones at all. Most women who take hormones do so only in the early portion of their postmenopausal years, so the risk of endometrial cancer following cessation of use might bear heavily on the overal risk/benefit evaluation. We analyzed data from a case-control study of women in western Washington (United States) to assess the magnitude of excess risk of endometrial cancer following discontinuation of estrogen use. Cases (n=661) consisted of women aged 45 to 74 diagnosed between 1985 and 1991 who resided in one of three counties in Washington State. Controls (n=865) were identified by random-digit dialing. Subjects were interviewed in-person to ascertain current and prior hormone use. The analysis was restricted to women who had not received combined estrogen-progestin therapy. Among women who had used unopposed estrogens at some time, risk of endometrial cancer declined as time since last use increased. Nonetheless, even among women who used these hormones for just a few years, the risk remained elevated by 30 to 70 percent almost a decade after cessation. These results, combined with those of most (but not all) other studies of this issue, suggest that a woman who has discontinued unopposed estrogen therapy may retain a small increased risk of endometrial cancer for a long period of time.Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, the Department of Epidemiology, University of Washington Department of Biostatistics University of Washington, Seattle, WA. Department of Epidemiology, University of Washington, Seattle, WA 98195, USA. This research was supported by US National Cancer Institute contracts R01 CA47749 and R35 CA39779.     

Tibolone and risk of gynecological hormone sensitive cancer

Risk of ovarian cancer with hormone therapy is associated with use of both unopposed estrogen therapy and combined estrogen–progestin therapy, whereas for endometrial cancer addition of continuous progestin decreases the estrogen induced increased risk. Less is known about risk with use of tibolone; a synthetic steroid with estrogenic, progestagenic and androgenic properties. We assessed these associations in a prospective cohort study, including all Danish women 50–79 years of age and followed 1995–2009. National Danish Registers captured individually updated exposure information, cancer cases including histology and confounding factors. Poisson regression analyses provided multiple adjusted incidence rate ratios (IRRs). More than 900,000 women were followed for 9.8 years on average; 4,513 were diagnosed with ovarian cancer and 6,202 with endometrial cancer. Compared to women never on postmenopausal hormone therapy, current users of tibolone had an increased IRR for ovarian cancer (1.42(95% confidence interval [CI], 1.01–2.00) and serous ovarian tumors (2.21(95%CI 1.48–3.32)). The risk increased with duration of use, particularly for serous ovarian tumors. Compared to never users, the IRR of endometrial cancer was 3.56(95%CI 2.94–4.32) among current users of tibolone and 3.80(95%CI 3.08–4.69) of Type I endometrial cancer. The steepest risk increase with duration of use was for Type I tumors. In conclusion, tibolone is associated with increased risk for ovarian and endometrial cancer overall; and particular the risk of serous ovarian tumors and Type I endometrial cancer. Because the associations are stronger with increasing durations of use – and for hormone sensitive tumors – the results seem indicative of causality.     

A polymorphism in CYP17 and endometrial cancer risk

Among women, the A2 allele of CYP17 has been associated with elevated levels of endogenous steroid hormones; however, it does not seem to be a strong independent risk factor for breast cancer. We assessed the association between the A2 allele of CYP17 and invasive endometrial cancer risk in a case-control study nested within the Nurses' Health Study cohort (cases: n = 184; controls: n = 554). We also evaluated whether endometrial cancer risk associated with CYP17 genotype was modified by established endometrial cancer risk factors. In addition, we further examined the relationship between CYP17 genotype and endogenous plasma steroid hormone levels among postmenopausal controls not using hormone replacement therapy (HRT). Women with the A2 allele of CYP17 were at decreased risk of endometrial cancer (A1/A1 genotype (reference); A1/A2 genotype: odds ratio, 0.89; 95% confidence interval, 0.62-1.27; A2/A2 genotype: odds ratio, 0.43; 95% confidence interval, 0.23-0.80; P trend, 0.02). We also observed the inverse association between the A2 allele and endometrial cancer risk to be stronger among women with a first-degree family history of endometrial and/or colorectal cancer (P for interaction, 0.05). Among 165 controls, we did not observe women with the A2 allele to have significantly elevated levels of any steroid hormone fraction. When these women were combined and analyzed with those women on whom we had previously examined the relationship between CYP17 genotype and circulating hormone levels (total n = 469), only modest associations were observed for the A2/A2 genotype and steroid hormone fractions estrone (versus A1/A1 genotype: +10.9%; P = 0.05) and estradiol (+8.5%; P = 0.17). These data suggest that the A2 allele of CYP17 decreases endometrial cancer risk, but has only weak effects on endogenous estrogen levels among postmenopausal women.     

PGR +331 A/G and increased risk of epithelial ovarian cancer.

Childbearing and use of oral contraceptives are known to lower the risk of ovarian cancer, and it has been suggested that progesterone or progestin exposures play a role in these associations. The effects of progesterone may be mediated in part through the progesterone receptor, which exists in two functionally distinct protein isoforms, hPR-A and hPR-B. It is known that individuals carrying the A allele of the progesterone receptor gene (PGR) polymorphism, +331 A/G (rs10895068), have greater production of the hPR-B receptor isoform. We therefore examined the association between PGR +331 A/G genotype and risk of ovarian cancer in a population-based study of 490 cases and 534 controls in the state of Connecticut. Adjusted for various reproductive and other factors, a statistically significant increased risk was seen for carriage of the A allele compared with GG genotype [odds ratio (OR), 1.68; 95% confidence interval (95% CI), 1.09-2.59]. When subjects were considered separately according to menopausal status, no increased risk with the A allele was seen for premenopausal women (OR, 0.96; 95% CI, 0.46-2.02) but significantly increased risk was found for postmenopausal women (OR, 2.31; 95% CI, 1.31-4.06). Similar increased risks particularly among postmenopausal women were seen for all histologic tumor types. These findings have been observed before for breast and endometrial cancer, although not for ovary, but still suggest that an hPR-B mechanism may be involved in ovarian neoplasia.     

Polycystic Ovary Syndrome and Risk of Endometrial Cancer: a Mini-Review

The polycystic ovary syndrome is the most common endocrinological disorder of reproductive age women with a prevalence of 5 to 8 %. The most common diagnostic criteria used for polycystic ovary syndrome are oligo- or an-ovulation, clinical and/ or biochemical signs of hyperandrogenism and polycystic ovaries. Hyperandrogenism results in increased estrogen levels and lack of cyclic progesterone due to anovulation and persistent stimulation of the endometrium may lead to endometrial hyperplasia or adenocarcinoma development. In this mini review, we aimed to evaluate the possible relationship between polycystic ovary syndrome and endometrial cancer.     

A prospective evaluation of insulin and insulin-like growth factor-I as risk factors for endometrial cancer.

Obesity is a major risk factor for endometrial cancer, a relationship thought to be largely explained by the prevalence of high estrogen levels in obese women. Obesity is also associated with high levels of insulin, a known mitogen. However, no prospective studies have directly assessed whether insulin and/or insulin-like growth factor-I (IGF-I), a related hormone, are associated with endometrial cancer while accounting for estrogen levels. We therefore conducted a case-cohort study of incident endometrial cancer in the Women's Health Initiative Observational Study, a prospective cohort of 93,676 postmenopausal women. The study involved all 250 incident cases and a random subcohort of 465 subjects for comparison. Insulin, total IGF-I, free IGF-I, IGF-binding protein-3, glucose, and estradiol levels were measured in fasting baseline serum specimens. Cox models were used to estimate associations with endometrial cancer, particularly endometrioid adenocarcinomas, the main histologic type (n = 205). Our data showed that insulin levels were positively associated with endometrioid adenocarcinoma [hazard ratio contrasting highest versus lowest quartile (HR(q4-q1)), 2.33; 95% confidence interval (95% CI), 1.13-4.82] among women not using hormone therapy after adjustment for age and estradiol. Free IGF-I was inversely associated with endometrioid adenocarcinoma (HR(q4-q1), 0.53; 95% CI, 0.31-0.90) after adjustment for age, hormone therapy use, and estradiol. Both of these associations were stronger among overweight/obese women, especially the association between insulin and endometrioid adenocarcinoma (HR(q4-q1), 4.30; 95% CI, 1.62-11.43). These data indicate that hyperinsulinemia may represent a risk factor for endometrioid adenocarcinoma that is independent of estradiol. Free IGF-I levels were inversely associated with endometrioid adenocarcinoma, consistent with prior cross-sectional data.     

Hormone replacement therapy after cancers

PURPOSE OF REVIEW: The role of female hormones in estrogen-dependent cancers has been debated for years. This is particularly true of breast cancer. Retrospective, case, and cohort control studies usually have suggested no influence. The Women's Health Initiative study in 2002, a prospective double-blind study, noted an increased risk of breast cancer if estrogen plus progesterone was given. In the estrogen-only arm of that study, a decreased (not significant) risk of breast cancer was noted. With this controversy, can estrogen be given safely to a woman who has been treated for breast cancer? The relation between endometrial cancer and unopposed estrogen is well established. With clear-cut evidence of this relation, is there evidence to suggest a role for replacement therapy in women who have been treated for endometrial cancer? RECENT FINDINGS: Several case-control and cohort studies have noted either no increased risk or actually less risk of recurrence in women taking estrogen after therapy after breast cancer. Although the general consensus is that such a recommendation is contraindicated, the data do not support this admonition. The current data suggest that replacement therapy can be given to the woman who has been treated for endometrial cancer. SUMMARY: There seems to be little if any risk in giving hormone replacement therapy to women who have had breast or endometrial cancer. There are no data to suggest that hormone replacement therapy is contraindicated in women who have been treated for cervical or ovarian cancer.     

Hormonal profiles in women with breast cancer (review)

The literature concerning endogenous hormonal profiles in women with breast cancer and breast-cancer risk has been critically reviewed. The many published reports have been divided into 11 groups, with each group centered on a particular hypothesis that has been either explicitly formulated by the authors of the reports or perceived by other workers as a unifying hypothesis in certain studies. The hypotheses reviewed are: the adrenal androgen insufficiency hypothesis, the anovulation/luteal inadequacy hypothesis, the estriol hypothesis, the ovarian androgen excess hypothesis, the thyroid dysfunction hypothesis, the prolactin hypothesis, the estrone hypothesis, the estrogen-window hypothesis, the estrogen-excess hypothesis, the melatonin hypothesis, and the estrogen hydroxylation hypothesis. It is concluded that there remain, at present, only four viable hypotheses: the hypotheses of increased risk with adrenal androgen deficiency, ovarian dysfunction (luteal inadequacy and excessive ovarian androgen secretion), increased 16 alpha-hydroxylation of estradiol, and the hypothesis of decreased risk with pregnancy-induced lowering of prolactin levels. Adrenal androgen deficiency seems to be pertinent only in premenopausal cancer patients, and may be a genetic defect. Ovarian dysfunction seems to be pertinent to both premenopausal and post-menopausal patients and may also have a strong genetic component. Increased estradiol hydroxylation likewise seems to have a genetic component. The prolactin effect differs from the others, in that it is clearly environmental, rather than genetic, and may represent a permissive effect rather than a true risk-promoting effect.     

The dose-effect relationship between 'unopposed' oestrogens and endometrial mitotic rate: its central role in explaining and predicting endometrial cancer risk

The 'unopposed oestrogen hypothesis' for endometrial cancer maintains that risk is increased by exposure to endogenous or exogenous oestrogen that is not opposed simultaneously by a progestagen, and that this increased risk is due to the induced mitotic activity of the endometrial cells. Investigation of the mitotic rate during the menstrual cycle shows that increases in plasma oestrogen concentration above the relatively low levels of the early follicular phase do not produce any further increase in the mitotic rate of endometrial cells. A modification of the unopposed oestrogen hypothesis which includes this upper limit in the response of endometrial cells to oestrogen is consistent with the known dose-effect relationships between endometrial cancer risk and both oestrogen replacement therapy and postmenopausal obesity; it also suggests that the mechanism by which obesity increases risk in premenopausal women involves progesterone deficiency rather than oestrogen excess, and that the protective effect of cigarette smoking may be greater in postmenopausal than in premenopausal women. Detailed analysis of the age-incidence curve for endometrial cancer in the light of this hypothesis suggests that there will be lifelong effects of even short duration use of exogenous hormones. In particular, 5 years of combination-type oral contraceptive use is likely to reduce a woman's lifetime risk of endometrial cancer by some 60%; whereas 5 years of unopposed oestrogen replacement therapy is likely to increase her subsequent lifetime risk by at least 90%; and even 5 years of 'adequately' opposed therapy is likely to increase subsequent lifetime risk by at least 50%.     

Body mass index, height, and the risk of ovarian cancer mortality in a prospective cohort of postmenopausal women.

Endogenous hormones may play a role in ovarian carcinogenesis. Postmenopausal obesity, although associated with higher circulating levels of estrogen and androgens, has not been linked consistently to ovarian cancer. The present study examined the relationship between body mass index (BMI), height, and ovarian cancer mortality among postmenopausal women in a large prospective mortality study of 300,537 women who were cancer free at enrollment in 1982 and had no history of hysterectomy or ovarian surgery. During 16 years of follow-up, 1,511 deaths occurred from ovarian cancer. Cox proportional hazard modeling was used to compute rate ratios (RRs) and to adjust for confounders. Ovarian cancer mortality rates were higher among overweight [BMI >/=25;RR, 1.16; 95% confidence interval (CI), 1.04-1.30] and obese women (BMI >/=30; RR, 1.26; 95% CI, 1.07-1.48) compared with women with BMI <25. Use of postmenopausal estrogens modified the association between BMI and ovarian cancer mortality (P = 0.05). The increased risk associated with obesity (BMI >/=30) was limited to women who never used postmenopausal estrogens (RR, 1.36; 95% CI, 1.12-1.66) and was not seen among ever users (RR, 0.93; 95% CI, 0.62-1.41). Height was positively associated with ovarian cancer mortality. Compared with women 152-156 cm tall, ovarian cancer mortality rates were lowest for the shortest women (RR, 0.72; 95% CI, 0.47-1.10 for women <152 cm) and highest for the tallest (RR, 1.41; 95% CI, 0.95-2.09 for women >/=177 cm). In this study, obesity and height appear to be independently associated with ovarian cancer mortality. The 36% increase in risk associated with obesity among women who had never used postmenopausal estrogens may have important public health implications because obesity is a growing problem in the United States.     

Is estrogen plus progestin menopausal hormone therapy safe with respect to endometrial cancer risk?

Given the strong link between use of unopposed estrogens and development of endometrial cancers, estrogens are usually prescribed with a progestin, particularly for women with intact uteri. Some studies suggest that sequential use of progestins may increase risk; however, the moderating effects of usage patterns or patient characteristics, including body mass index (BMI), are unknown. We evaluated menopausal hormone use and incident endometrial cancer (n = 885) in 68,419 postmenopausal women with intact uteri enrolled in the National Institutes of Health‐American Association of Retired Persons Diet and Health study. Participants completed a risk factor questionnaire in 1996–1997 and were followed up through 2006. Hazard rate ratios (RRs) and 95% confidence intervals (CIs) were estimated using Cox regression. Among 19,131 women reporting exclusive estrogen plus progestin use, 176 developed endometrial cancer (RR = 0.88; 95% CI = 0.74–1.06). Long‐duration (≥10 years) sequential (<15 days progestin per month) estrogen plus progestin use was positively associated with risk (RR = 1.88; 95% CI = 1.36–2.60], whereas continuous (>25 days progestin per month) estrogen plus progestin use was associated with a decreased risk (RR = 0.64; 95% CI = 0.49–0.83). Increased risk for sequential estrogen plus progestin was seen only among thin‐to‐normal weight women (BMI < 25 kg/m²; RR = 2.53). Our findings support that specific categories of estrogen plus progestin use increases endometrial cancer risk, specifically long durations of sequential progestins, whereas decreased endometrial cancer risk was observed for users of short‐duration continuous progestins. Risks were highest among thin‐to‐normal weight women, presumably reflecting their lower endogenous estrogen levels, suggesting that menopausal hormones and obesity increase endometrial cancer through common etiologic pathways.     

CYP19 (aromatase) haplotypes and endometrial cancer risk

Endogenous estrogen exposure is an important determinant of endometrial cancer risk. Aromatase, encoded by CYP19, catalyzes the aromatization of androstenedione and testosterone to estrone and estradiol, respectively. Several common genetic polymorphisms in CYP19 have been identified, including a TCT insertion/deletion and a (TTTA)(n) repeat polymorphism in intron IV as well as a 3'UTR C/T polymorphism. We evaluated these 3 polymorphisms plus an additional 9 noncoding polymorphisms as individual genotypes and predicted haplotypes as risk factors for endometrial cancer using a nested case-control study design. Invasive endometrial cancer cases (n = 222) and matched controls (n = 666) were identified among participants in the Nurses' Health Study who had provided a blood sample in 1989-1990 (n = 32,826). We estimated haplotypes from unphased genotype data spanning > 123 kb of CYP19. Six haplotypes constructed from 10 SNPs were estimated with a frequency > or = 5%. The highest prevalence haplotype (33% among cases, 28% among controls) was significantly associated with endometrial cancer risk (p = 0.03). Loci with variant alleles that comprise the risk haplotype were independently associated with endometrial cancer, with relative risk estimates ranging from 1.68 (95% CI 1.13-2.48) to 2.07 (95% CI 1.33-3.23), comparing variant allele carriers to wild-type homozygotes. We observed significant interactions between menopausal status and 2 of the high-risk loci (p = 0.03 and p < 0.01), with > 2-fold increased risk for variant allele carriers who were postmenopausal but no association between genotype and endometrial cancer among premenopausal women. We evaluated associations between CYP19 haplotypes and plasma steroid hormone levels. The haplotype associated with endometrial cancer risk is also significantly associated with the ratios of estrone to androstenedione and estradiol to testosterone, the products and substrates of the enzyme aromatase, encoded by CYP19. Our data suggest that there is a high-frequency CYP19 haplotype related to higher estrogen to androgen ratios and increased risk of endometrial cancer and that this association may primarily pertain to postmenopausal women.     

Hormone Replacement Therapy: The Debate over the Risks and Benefits To Women,from Breast Cancer To Quality of Life

The use of hormone replacement therapy, unopposed estrogen or combined estrogen plus progestin, for postmenopausal women has been debated for many years. It has been used for relief from menopausal symptoms and for protective measures from chronic conditions, such as cardiovascular disease and osteoporosis. There have been observational studies and randomized clinical trials undertaken to determine the benefits and risks of these therapies. There are no definite answers among the trials and there are some discrepancies. The major findings, however, have been an increase in breast and endometrial or ovarian cancer, an increase in coronary heart disease, stroke and thromboembolism, a decrease in colorectal cancer, a decrease in bone fractures and an improvement in menopausal symptoms. The current, overall recommendation to women is not to use hormone replacement therapy as a long-term protective measure, but after individual consideration, it may be appropriate on a short-term basis for relief of menopausal symptoms.