Endometrial cancer: how does cigarette smoking influence the risk of women under age 55 years having this tumor?

Cigarette smoking and endometrial carcinoma risk: the role of effect modification and tumor heterogeneity

PURPOSE

The inverse relationship between cigarette smoking and endometrial carcinoma risk is well established. We examined effect modification of this relationship and associations with tumor characteristics in the National Institutes of Health-AARP Diet and Health Study.

METHODS

We examined the association between cigarette smoking and endometrial carcinoma risk among 110,304 women. During 1,029,041 person years of follow-up, we identified 1,476 incident endometrial carcinoma cases. Multivariable Cox proportional hazards regression models were used to estimate relative risks (RRs) and 95 % confidence intervals (CIs) for the association between smoking status, years since smoking cessation, and endometrial carcinoma risk overall and within strata of endometrial carcinoma risk factors. Effect modification was assessed using likelihood ratio test statistics. Smoking associations by histologic subtype/grade and stage at diagnosis were also evaluated.

RESULTS

Reduced endometrial carcinoma risk was evident among former (RR 0.89, 95 % CI 0.80, 1.00) and current (RR 0.65, 95 % CI 0.55, 0.78) smokers compared with never smokers. Smoking cessation 1-4 years prior to baseline was significantly associated with endometrial carcinoma risk (RR 0.65, 95 % CI 0.48, 0.89), while cessation ≥ 10 years before baseline was not. The association between smoking and endometrial carcinoma risk was not significantly modified by any endometrial carcinoma risk factor, nor did we observe major differences in risk associations by tumor characteristics.

CONCLUSION

The cigarette smoking-endometrial carcinoma risk relationship was consistent within strata of important endometrial carcinoma risk factors and by clinically relevant tumor characteristics.

Active and passive cigarette smoking and the risk of endometrial cancer in Poland

BACKGROUND

Epidemiological studies have consistently reported that active cigarette smoking is inversely associated with endometrial cancer risk. However, dose-response relationships with quantitative measures of active smoking or passive smoking remain less clear.

METHODS

Data on lifetime active and passive smoking were collected for 551 endometrial cancer cases and 1925 controls in a population-based case-control study conducted during 2001-2003 in Poland (Warsaw and Łódz).

RESULTS

Compared with never active smokers, active current (Odds Ratio (OR)=0.51, 95% Confidence Interval (CI): 0.39, 0.68) and former smokers (OR=0.60, 95% CI: 0.45, 0.80) were at a statistically significantly decreased risk. We did not observe statistically significant inverse dose-response relationships with increasing exposure with duration and cumulative measures. However, there was some indication that the highest category of number of years (OR=0.35, 95% CI: 0.23-0.55), intensity (OR=0.41, 95% CI: 0.24-0.69), and dose (OR=0.38, 95% CI: 0.24-0.60) of smoking among current smokers had the greatest inverse association compared to never smokers. Our data did not support the presence of an inverse association with passive smoking among never active smokers (OR=0.92; 95% CI: 0.65, 1.29).

CONCLUSION

Our results support that long-term and heavy smoking among current smokers strongly influence endometrial cancer risk.

Cigarette smoking and the risk of endometrial cancer: a meta-analysis

OBJECTIVE

Epidemiologic findings are inconsistent concerning the association of endometrial cancer risk with cigarette smoking. We conducted a meta-analysis of epidemiologic studies to examine this relation.

METHODS

A systematic literature search up to June of 2007 was performed in MEDLINE and EMBASE. Study-specific risk estimates were pooled using a random-effects model.

RESULTS

Ten prospective and 24 case-control studies were included in the analysis of the effect of ever smoking. Ever smoking was statistically significantly associated with a reduced risk of endometrial cancer among prospective studies (relative risk 0.81; 95% confidence interval [CI], 0.74-0.88) and case-control studies (odds ratio 0.72; 95% CI, 0.66-0.79). The inverse association was significant among current and former smokers. Six prospective and 6 case-control studies were included in the quantitative analysis. We noted that an increase in smoking of 20 cigarettes per day was statistically significantly associated with 16% and 27% reduced risks of endometrial cancer in prospective and case-control studies, respectively. We also found that cigarette smoking was significantly associated with a decreased risk of endometrial cancer among postmenopausal women (relative risk 0.71; 95% CI, 0.65-0.78) but not among premenopausal women. In addition, the risk reduction seemed to be stronger among hormone replacement therapy users than nonusers.

CONCLUSION

Cigarette smoking was found to be significantly associated with a reduced risk of endometrial cancer, especially among postmenopausal women.

Relationships of uterine and ovarian tumors to pre-existing chronic conditions

OBJECTIVE

Several chronic diseases have been hypothesized to affect the risk of subsequent gynecologic malignancies, possibly through shared hormonal mechanisms.

METHODS

Using record linkage techniques, we assessed the relationships between hospital and outpatient admissions for gallbladder disease, diabetes, hypertension, thyroid diseases and obesity and the subsequent development of uterine and ovarian cancers in Denmark between 1978 and 1998. Based on a subsample of more than 99,000 women, including 1398 uterine and 2491 ovarian cancers, we derived relative risks (RRs) and 95% confidence intervals (CIs) associated with overall and histology-specific cancer risks after adjustment for age, calendar time and reproductive characteristics.

RESULTS

Uterine cancers were related to previous diagnoses of thyroid diseases (RR=1.52, 95% CI 1.17-1.98) and obesity (2.05, 1.40-3.00). Associations with diabetes were confounded by obesity, but there were some elevations in risk for subjects diagnosed with obesity prior to age 45 (RRs 1.66-1.79). Although the "usual types" of endometrial cancer largely accounted for the observed associations, there was some evidence that uterine sarcomas (n=137) were related to prior diagnoses of thyroid diseases (2.78, 1.41-5.50). In contrast, ovarian cancers were not strongly related to most documented chronic diseases. Serous carcinomas were associated with gallbladder diseases of short durations, but detection bias or misdiagnosis probably accounts for this association. An association of obesity and endometrioid ovarian cancer was not identified.

CONCLUSIONS

Uterine cancers, including sarcomas, appear to be influenced by selected chronic diseases. Further attention should focus on possible biologic mechanisms underlying observed associations with thyroid diseases and obesity.

Cigarette smoking and the risk of endometrial cancer

Epidemiological studies have shown that cigarette smoking is associated with a reduced risk of endometrial cancer, in contrast to the increased risks observed with many other non-respiratory-tract cancers, including those of the bladder, pancreas, and cervix uteri. Some studies of endometrial cancer suggest that the inverse association with smoking is limited to certain groups of women, such as those who are postmenopausal or those taking hormone-replacement therapy. The biological mechanisms that might underlie this association remain unclear, although several have been proposed, including an antioestrogenic effect of cigarette smoking on circulating oestrogen concentrations, a reduction in relative bodyweight, and an earlier age at menopause. We have examined the evidence for an association between cigarette smoking and risk of endometrial cancer, including studies related to the proposed biological mechanisms.

A prospective cohort study of cigarette smoking and the risk of endometrial cancer

Case-control studies have shown inverse associations between cigarette smoking and endometrial cancer risk. However, two small prospective cohort studies have not clearly supported an association. Moreover, quantitative measures of smoking have been examined infrequently. Our aim was to study the association between smoking and endometrial cancer risk in a large prospective cohort. We used proportional hazards models to estimate hazard ratios relating cigarette smoking to endometrial cancer risk among 70 591 women aged 40-59 years at recruitment into a randomised controlled trial of mammography screening for breast cancer. During an average of 10.6 years of follow-up (751 833 person-years), a total of 403 women were diagnosed with incident endometrial cancer. We found that a reduced endometrial cancer risk was evident only among women who currently smoked 20 cigarettes per day or more (hazard ratio=0.62, 95% CI=0.42-0.92, P for trend=0.03). There was some suggestion of an inverse association with smoking duration, but this was less clear. The association did not vary with menopausal status, relative body weight, or the use of hormone replacement therapy, but it appeared to be stronger among parous than nulliparous women. The underlying biological mechanisms of this association remain unclear.

Risk factors among young women with endometrial cancer: a Danish case-control study

OBJECTIVE

This study was undertaken to identify and quantify risk factors for endometrial cancer among young women.

STUDY DESIGN

This case-control study included all Danish women <50 years old who had endometrial cancer diagnosed during the period 1987 to 1994. A total of 237 case patients and 538 population control subjects matched with the case patients for age and residence were included in the analysis.

RESULTS

Women with a family history of endometrial cancer had an odds ratio for endometrial cancer of 2.1 (95% confidence interval, 1.1-3.8)). Completion of 1 term pregnancy implied an odds ratio of 0.6 (95% confidence interval, 0.3-1.1). The risk of endometrial cancer decreased significantly with increasing age at first birth and with the number of induced abortions. Use of oral contraceptives for 1 to 5 years decreased the risk of endometrial cancer (odds ratio, 0.2; 95% confidence interval, 0.1-0.3). The odds ratio for endometrial cancer among women who received hormone replacement therapy for 1 to 5 years was 3.1 (95% confidence interval, 1.4-7.0). Body mass index was not demonstrated to be an independent risk factor in this study. The protective impacts of the different exposures (risk factors) can be expressed as etiologic fractions, which indicate how much each exposure reduces the occurrence of endometrial cancer compared with a situation without the existence of that particular exposure. These fractions were as follows: oral contraceptive use for > or =1 year, -45%; 2 term pregnancies, -88%; age > or =30 y when giving birth for the first time, -38%; and a history of incomplete pregnancy, -16%.

CONCLUSION

A number of risk factors for endometrial cancer are common to premenopausal and postmenopausal women: family history, reproductive history, hormone replacement therapy, and the use of oral contraceptives. Among young women reproductive variables imply the greatest prophylactic potential.

Smoking and hormone-related disorders

Through its antiestrogenic effect, cigarette smoking is linked to a variety of hormone-related disorders, both benign and malignant. Diseases that depend on this hormone for growth and development tend to be less common among smokers, such as endometrial cancer and uterine fibroids. Some normal, estrogen-dependent physiologic processes are affected by smoking, making osteoporosis and premature menopause more common among women who smoke. In other disorders, the link between sex hormone levels, cigarette smoking, and disease development is less clear.

Hypertension and hormone-related neoplasms in women

The relation between hypertension and the risk of selected hormone-related neoplasms in women was investigated in a network of case-control studies conducted in Italy during 1983-1996. Cases were women younger than 75 years with histologically confirmed cancer of the breast (n=3406), endometrium (n=745), ovary (n=970), and thyroid (n=145). Controls were 3054 women admitted in the same geographic area for acute, nonneoplastic, non-hormone-related diseases. Odds ratios (ORs) of treated hypertension were computed after allowance for sociodemographic factors, smoking habits, alcohol consumption, parity, menopausal status, and body mass index (BMI) by means of unconditional logistic regression. The ORs were 1.2 (95% CI, 1.1 to 1.4) for breast cancer and 1.6 (95% CI, 1.3 to 1.9) for endometrial cancer, and the elevated ORs persisted after >/=5 years since diagnosis of hypertension. No significant association was observed for ovarian and thyroid cancer. For breast cancer, the association was apparently stronger at age 55 years or over and consequently after menopause. No appreciable effect modification was evident for endometrial cancer. Allowance for BMI did not explain the association of postmenopausal breast cancer and endometrial cancer with hypertension. The OR of postmenopausal breast cancer was 1.5 (95% CI, 1.1 to 2.0) in hypertensive women with BMI >/=30 kg/m(2) compared with normotensive women with BMI <25 kg/m(2). The corresponding figure for all endometrial cancers was 4.9 (95% CI, 3. 4 to 6.9). Even in the absence of a clear understanding of biological mechanisms, the definition of a role of hypertension on female hormone-related cancers can have relevant implications on individual risk assessment.

Estrogen and aryl hydrocarbon responsiveness of ECC-1 endometrial cancer cells

ECC-1 endometrial cancer cells express estrogen receptor alpha (ER(alpha)), and 17beta-estradiol (E2) induces cell proliferation, cathepsin D mRNA levels, and reporter gene activity in cells transiently transfected with constructs derived from the human cathepsin D and creatine kinase B (pCD and pCKB, respectively) gene promoters. The comparative antiestrogenic activity of aryl hydrocarbon receptor (AhR) agonists and ER(alpha) antagonists were also determined in these endometrial cancer cells. A functional AhR was expressed in ECC-1 cells and AhR agonists including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) inhibited E2-induced cell proliferation and transactivation. This was comparable to inhibitory AhR-ER crosstalk in breast cancer cell lines. The pure ER antagonist ICI 182,780 also exhibited antiestrogenic activity in ECC-1 cells; however, the results obtained for 4'-hydroxytamoxifen were response-specific. 4'-Hydroxytamoxifen alone did not induce ECC-1 cell proliferation but completely inhibited E2-induced cell proliferation. 4'-Hydroxytamoxifen primarily exhibited ER antagonist activities in transactivation assays and this contrasted to the predominant ER agonist responses observed in other endometrial cancer cell lines. The unique cellular context of ECC-1 cells was confirmed using pCKB and constructs expressing wild-type ER or ER variants expressing activation function 1 (AF1) or AF2 (ER-AF1 and ER-AF2, respectively). 4'-Hydroxytamoxifen did not induce reporter gene activity in cells cotransfected with pCKB and ER-AF1 or ER-AF2; however, in cotreatment studies (4'-hydroxytamoxifen plus E2), 4'-hydroxytamoxifen inhibited E2-induced transcriptional activation by ER-AF1 or ER-AF2. Thus, the primarily antiestrogenic activity observed for 4'-hydroxytamoxifen in ECC-1 cells may be related to the inability to activate gene expression through AF1-dependent pathways.

Interactions between hormones and chemicals in breast cancer

Development of breast cancer in women is dependent on diverse factors, including genetic predisposition, exposure to both exogenous and endogenous chemicals, which can modulate initiation, promotion and progression of this disease, and the timing of exposure to these agents. Several compounds--including 16 alpha-hydroxyestrone (16 alpha-OHE1), catecholestrogens, and aromatic amines--have been proposed as initiators of mammary carcinogenesis in humans; however, their role as genotoxins is unconfirmed. Lifetime exposure to estrogens has been established as an important risk factor for breast cancer, and it has been suggested that xenoestrogens may directly add to the hormonal risk or indirectly increase risk by decreasing 2-hydroxyestrone (2-OHE1)/16 alpha-OHE1 metabolite ratios. Results of recent studies suggest that chemical-induced modulation of 2-OHE1/16 alpha-OHE1 metabolite ratios is not predictive of xenoestrogens or mammary carcinogens. Moreover, based on current known dietary intakes of natural and xenoestrogenic/antiestrogenic chemicals, it is unlikely that xenoestrogens contribute significantly to a woman's overall lifetime exposure to estrogens. More information is required on the identities and serum levels of both natural and xenoendocrine active compounds, their concentrations in serum, and the mammary gland and levels of these compounds at critical periods of exposure.

Inhibition of estrogen-induced progesterone receptor in MCF-7 human breast cancer cells by aryl hydrocarbon (Ah) receptor agonists

17 beta-Estradiol (E2) induces progesterone receptor (PR) binding, immunoreactive protein, nuclear PR formation and PR mRNA levels in MCF-7 human breast cancer cells. Gel mobility shift analysis of nuclear extracts from E2-treated cells also exhibited a higher intensity retarded band associated with formation of a PR complex with a consensus [32P]progesterone/glucocorticoid responsive element. In contrast, 1 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alone did not alter or decrease these same responses in MCF-7 cells; however, in cells co-treated with 1 nM TCDD plus 1 nM E2, TCDD significantly inhibited all the E2-induced responses. Scatchard analysis of PR binding demonstrated that TCDD decreased the number of E2-induced PR cellular binding sites but not the binding affinity of the PR for a radiolabeled promegestrone. In parallel studies, 3-methylcholanthrene, a prototypical polynuclear aromatic hydrocarbon, also inhibited E2-induced PR binding and immunoreactive protein. For a series of halogenated aromatics including 2,3,7,8- and 1,2,7,8-tetrachlorodibenzofuran, 1,3,7,8-TCDD and 6-methyl-1,3,8-trichlorodibenzofuran, their rank order potency for inhibiting E2-induced PR binding paralleled their rank order binding to the aryl hydrocarbon (Ah) receptor. These results support a role for the Ah receptor in mediating the antiestrogenic activity of polynuclear and halogenated aromatic hydrocarbons and illustrate cross-talk between the Ah and estrogen receptor signal transduction pathways.

Cigarette smoking and steroid hormones in women

Epidemiological evidence has suggested that cigarette smoking has an anti-oestrogenic effect in women, but the effects of smoking on steroid hormone metabolism are not fully understood. We compared serum concentrations of oestradiol, progesterone (luteal phase) and dehydroepiandrosterone sulphate (DHEA-S), and urinary excretion rates of six steroids of predominantly adrenal origin, in healthy premenopausal and postmenopausal female smokers and non-smokers. Serum concentrations of oestradiol, progesterone and DHEA-S did not differ between smokers and non-smokers by greater than 5%, and none of these differences was statistically significant. Mean urinary excretion rates of androsterone, aetiocholanolone, DHEA, 11-keto-aetiocholanolone, 11-hydroxyandrosterone and 11-hydroxyaetiocholanolone were very similar in smokers and non-smokers in premenopausal women, but were from 2-44% higher in smokers than non-smokers in postmenopausal women. The difference was statistically significant only for 11-hydroxyandrosterone. These results confirm previous reports that cigarette smoking does not affect serum oestradiol in premenopausal or postmenopausal women, but provide only weak evidence to support previous findings of increased levels of some adrenal steroids in postmenopausal women smokers. The mechanism for the apparent anti-oestrogenic effect of cigarette smoking remains unclear.

A population-based case-control study of endometrial cancer in Shanghai, China

A case-control study of 268 patients with endometrial cancer and 268 population controls was conducted during 1988-1990 in Shanghai, China, to evaluate etiologic factors in a population whose risk had not been substantially altered by the use of exogenous estrogens. In spite of this, the major risk factors resembled those found in other studies. The risk of endometrial cancer was significantly elevated among nulligravidas (OR = 5.4, 95% CI = 2.0-14.6) and decreased with number of pregnancies (p less than 0.01). Late age at menopause was associated with increased risk, while early age at menarche was unrelated. Use of oral contraceptives for more than 2 years was associated with a reduction in endometrial cancer risk (OR = 0.4, 95% CI = 0.1-1.2), while short-term use of oral contraceptives and other methods of contraception were unrelated. Obesity was a strong predictor of risk, with women in the highest quartile of weight having 2.5 times the risk of those in the lowest quartile. In contrast to many other studies, cigarette smokers were at elevated risk (OR = 1.7, 95% CI = 0.9-3.0). Risk was also elevated among women reporting a history of gall-bladder disease, polycystic ovaries, menstrual symptoms, and non-estrogen hormone use.

The epidemiology of endometrial cancer

The descriptive and analytical epidemiology of endometrial cancer is reviewed. Over the last few decades, age-standardized incidence rates have been rising in several countries. The rise has been even greater in terms of absolute numbers of cases, and hence public health implications, due to the aging of the population. Although endometrial cancer rates were found to be higher in richer countries and urban populations, there is now evidence of some changes in the socioeconomic determinants of the disease in developed countries. In etiological terms, any factor that increases exposure to unopposed estrogens (such as menopausal replacement treatment, obesity, and irregular menstrual cycles) tends to increase the risk of the disease, while factors that decrease exposure to estrogens or increase progesterone levels (such as oral contraceptives or smoking) tend to be protective. Less well defined, or more difficult to explain in biological terms, is the role of other factors, such as births, miscarriages, or diabetes and hypertension, and only suggestive evidence is available on diet from analytical epidemiology. The data reviewed herein are discussed in terms of models of carcinogenesis, as well as attributable risks and public health implications.

Reproductive factors and risk of endometrial cancer

The role of reproductive factors in endometrial cancer risk has been analyzed in a case-control study conducted since 1983 in the greater Milan area on 568 women (cases) with histologically confirmed endometrial cancer and 1925 women (controls) who were admitted for acute, nonmalignant, hormonal, gynecologic conditions to hospitals that cover a comparable catchment area. Compared with nulliparous women, parous women had a 30% lower risk of endometrial cancer, but there was no evidence of a decline in risk with increasing number of births. The risk of the disease decreased with number of spontaneous or induced abortions; the multivariate relative risk estimates were, compared respectively with no spontaneous or induced abortions, 0.5 for women with two or more spontaneous abortions and 0.3 for women with two or more induced abortions; both trends in risk were statistically significant. When parous women only were considered, no association emerged between endometrial cancer and age at first birth, but the risk decreased with increasing age at last birth: compared with women whose last birth occurred before age 25, the relative risk was 0.5 for women who were greater than or equal to 35 years old at last birth, and the multivariate trend in risk was statistically significant. For most of the reproductive factors that were considered, the risk estimates tended to be greater at younger age or among premenopausal women and to flatten off in subsequent strata of age. An association between endometrial cancer and age at first birth was observed in women who were less than or equal to 49 years old, but not in older groups. The observation that later age at last birth as well as later first birth in younger women decreases the risk of endometrial cancer suggests a short-term protective effect of pregnancy. This finding is consistent with a late-stage (promotional) effect of reproductive factors on endometrial carcinogenesis.

Endometrial carcinoma and its precursors: early detection and treatment

Endometrial carcinoma is the most frequent genital neoplasia in women. Precursors of this condition include endometrial hyperplasia, particularly when cytologic atypia occurs. Among the frequent early clinical manifestations of endometrial carcinoma is abnormal uterine bleeding that must be differentiated from bleeding associated with benign conditions. Early detection of endometrial carcinoma and its precursors in women at risk is the best prophylactic measure in the final therapeutic outcome. In this review, the accuracy of methods of early diagnosis of endometrial carcinoma and its precursors is assessed, in order to provide early therapy and optimum prognosis. The epidemiology of endometrial carcinoma, as well as the risk factors for the development of this neoplasia, are also reviewed. A histologic classification of endometrial hyperplasia and carcinoma of the endometrium, based on current theories of histopathogenesis, is included.

The antiestrogenic effect of cigarette smoking in women

Epidemiologic results indicate that women who smoke cigarettes are relatively estrogen-deficient. Smokers have an early natural menopause, a lowered risk of cancer of the endometrium, and an increased risk of some osteoporotic fractures. Moreover, women who smoke may have a reduced risk of uterine fibroids, endometriosis, hyperemesis gravidarum, and benign breast disease. Several possible mechanisms for these effects have been identified. Smoking does not appear to be clearly related to estradiol levels, at least in postmenopausal women, although levels of adrenal androgens are increased. Moreover, smoking appears to alter the metabolism of estradiol, leading to enhanced formation of the inactive catechol estrogens.

A case-control study of cancer of endometrium in Athens

Eighty-three women with invasive adenocarcinoma of the endometrium and 164 control women hospitalized for various orthopedic conditions were interviewed regarding demographic, reproductive, socio-economic and biomedical characteristics, including their use of tobacco, drugs and exogenous estrogens. The data were analyzed by modelling rate ratio (r) through multiple logistic regression. The main results were as follows: women with invasive adenocarcinoma of the endometrium had earlier menarche (r = 0.82 for every additional year; one-tailed p approx. 0.04), later menopause (r = 1.50 for a 5-year difference; one-tailed p approx. 0.004), and fewer live-born children (r = 0.86 for every additional child; one-tailed p approx. 0.08); they were also taller (r = 1.33 for a 5-cm difference; one-tailed p approx 0.03), whereas weight, adjusted for height, was not a statistically significant risk indicator (one-tailed p approx. 0.38). Regular use of combination oral contraceptives was associated with a reduced risk of endometrial cancer (r = 0.56), whereas intake of menopausal estrogens for more than 6 months was associated with an increased risk (r = 2.04); however, because of the low frequency of use of exogenous estrogen preparations in Greece, neither of these 2 results was statistically significant. Tobacco smoking was associated with a significantly reduced risk of endometrial cancer; smoking 15-20 cigarettes per day for 20 years was associated with a rate ratio of 0.49 (one-tailed p approx. 0.03). The protective effect of tobacco smoking was evident only among post-menopausal women. These results indicate that the risk profile of endometrial cancer is similar in high-risk and low-risk countries, and underline the importance of unopposed estrogenic stimulation in the pathogenesis of this cancer.

Increased urinary catechol estrogen excretion in female smokers

Premenopausal female smokers show significantly increased estrogen 2-hydroxylation, which may account in part for the anti-estrogenic effects of cigarette smoking. We have measured five major urinary estrogens, including estradiol (E2), estrone (E1), 16 alpha-hydroxyestrone (16 alpha OHE1), estriol (E3), and 2-hydroxyestrone (2OHE1), in premenopausal female smokers and non-smokers, to determine whether increased C-2 hydroxylation affected the urinary excretory patterns in these subjects. While total measured estrogen excretion in the follicular phase did not differ significantly between the two groups, urinary 2OHE1 among the smokers constituted a significantly greater proportion of the total (31.1 vs 18.2%, P less than 0.02). This difference was largely caused by significantly increased urinary 2OHE1 and decreased E3 observed in smokers. A urinary catechol estrogen index, defined by [2OHE1]/[E3], was significantly elevated in smokers compared with non-smokers (1.67 +/- 0.21 vs 0.56 +/- 0.08, P less than 0.001), and this urinary index correlated strongly with radiometrically determined estrogen 2-hydroxylation (r = 0.84, P less than 0.01). Ratios of the various estrogen metabolites did not vary substantially throughout the menstrual cycle. Urinary estrogen indices as described here may therefore be useful in demonstrating differences in estrogen metabolism, specifically 2-hydroxylation vs 16 alpha-hydroxylation, in selected populations.

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%.

Cigarette smoking and the risk of endometrial cancer

The risk of endometrial cancer in relation to cigarette consumption was evaluated in a hospital-based case-control study of breast and genital neoplasms conducted in Milan, northern Italy. For the present analysis, 357 women (cases) with histologically confirmed endometrial cancer were compared to a group of 1122 women (controls) admitted for a large spectrum of acute conditions unrelated to smoking or to any of the known or potential risk factors for endometrial cancer. Compared with never-smokers, the multivariate relative risk estimates were for current 0.45 [95% confidence interval (CI) = 0.30-0.70] and 0.86 (95% CI = 0.50-1.46) for ex-smokers. The negative association of endometrial cancer with current smoking was not influenced by menopausal status as well as by other major identified potential confounding factors, i.e. menstrual and reproductive history, body mass index, oral contraceptive or estrogen replacement therapy use and family gynecologic cancer history. However, there was no evidence of a dose-risk effect, since the relative risks were similar in moderate and heavy smokers. The present study confirms that smoking is less frequent in cases hospitalized for endometrial cancer than in a comparison group of patients with non-smoking-related acute conditions. This negative association is perhaps explained in terms of reduced estrogen levels in smokers, though the influence and the importance of some uncontrolled selection bias (due, for instance, to longer hospital stay of smokers even when admission diagnosis was for non-smoking-related conditions) cannot be ruled out.

Cigarette smoking and the risk of female reproductive cancer

An epidemiologic study was conducted to evaluate the relationship between cigarette smoking and the risk of breast, endometrial, and ovarian cancers. Results indicated a clear reduction of risk for endometrial cancer among women aged 50 years and older who smoke cigarettes. Risks were significantly reduced among moderate smokers (odds ratio = 0.6), heavy smokers (odds ratio = 0.4), and former smokers (odds ratio = 0.6). No association was observed among women under age 50 years. When the relationship between cigarette smoking and breast cancer was investigated, no statistically significant association between cigarette smoking and the risk of breast cancer was observed except among women greater than 50 years who were light smokers only. There was also a nonstatistically significant increase in risk among younger women smoking more than two packs of cigarettes a day (odds ratio = 2.0), but overall there was no evidence of any relationship. Similarly, no association between ovarian cancer and cigarette smoking was apparent, although there was a nonsignificant increase in risk among women under age 50 years who smoked 40 or more cigarettes a day or were exsmokers.

Smoking, body weight, and early-stage endometrial cancer

The effect of cigarette smoking on the risk of early-stage endometrial cancer was evaluated in a population-based case-control study of women aged 40 to 69 years from upstate New York. Two hundred women with early-stage endometrial cancer diagnosed between 1979 and 1981, and 200 matched community controls were interviewed in person and asked about smoking habits and other risk factors. Statistical analysis revealed a significant decline in relative risk with increased smoking (P less than 0.05). This effect strongly modified the well-known increase in risk with body weight. Among smokers risk did not increase with body weight, whereas among nonsmokers risk increased rapidly with body weight, especially among nonsmokers in whom the peripheral conversion of androgens was the primary source of serum estrogen. Despite this apparent reduced risk for endometrial cancer, smoking remains a major health hazard for women as well as men.

Endometrial carcinoma occurring in patients under the age of 45 years

Endometrial adenocarcinoma is frequently unsuspected in women under the age of 45 years by the gynecologist or the pathologist, but it does occur. Twenty-seven cases of endometrial adenocarcinoma in this age group, from 1980 to 1985, were reviewed clinically and pathologically. Five cases were excluded by histologic examination. Obesity and abnormal vaginal bleeding were shown to be risk factors. Endometrial screening is to be encouraged. This cancer may arise de novo rather than from a premalignant precursor. Implications of this neoplasm for the premenopausal woman are considered.

Postmenopausal smoking, estrogen replacement therapy, and the risk of endometrial cancer

Previous studies of the association between cigarette smoking and endometrial cancer have yielded inconsistent results. There is some evidence that this discrepancy may be explained by differences in menopausal status between the groups of women studied. We addressed the issue of the effects of postmenopausal smoking on endometrial cancer risk using data from the Cancer and Steroid Hormone Study, a multicenter, population-based, case-control study of gynecologic cancers in the United States. We found that smoking after natural menopause is associated with a 70% reduced risk of endometrial cancer among estrogen users and a 50% reduced risk among nonusers of estrogen. These findings are consistent with previously proposed biologic effects of smoking on estrogen metabolism, which may have important clinical implications.

Increased 2-hydroxylation of estradiol as a possible mechanism for the anti-estrogenic effect of cigarette smoking

Epidemiologic data indicate that cigarette smoking is associated with an important anti-estrogenic effect, and increased hepatic metabolism has been suggested as a possible mechanism. We examined the hypothesis that cigarette smoking in women induces an increase in estradiol 2-hydroxylation. This irreversible metabolic pathway yields 2-hydroxyestrogens, which possess minimal peripheral estrogenic activity and are cleared rapidly from the circulation. We found a significant increase in estradiol 2-hydroxylation in premenopausal women who smoked at least 15 cigarettes per day. The extent of the reaction (mean +/- SEM) was 53.6 +/- 2.2 percent among 14 smokers and 35.1 +/- 1.8 percent among 13 nonsmoking controls--an increase of approximately 50 percent (P less than 0.001). The extent of 2-hydroxylation among five smokers did not vary during the follicular and luteal phases of their menstrual cycles. In addition, urinary excretion of estriol relative to estrone was significantly decreased among smokers (P less than 0.01), providing evidence that the smoking-induced increase in 2-hydroxylation diminishes the competing metabolic pathway involving 16 alpha-hydroxylation. This study demonstrates that smoking exerts a powerful inducing effect on the 2-hydroxylation pathway of estradiol metabolism, which is likely to lead to decreased bioavailability at estrogen target tissues. Elucidation of the mechanism responsible for smoking-induced changes in 2-hydroxylation may be useful in the development of strategies to reduce the risk of hormone-dependent tumors.

Cigarette smoking and the risk of endometrial cancer

Because of evidence of reduced estrogen excretion in the urine of women who smoke cigarettes and evidence linking estrogen levels to the risk of cancer of the female reproductive system, we evaluated the risk of endometrial cancer in relation to cigarette use in a hospital-based case-control study of 510 women with endometrial cancer (cases) and 727 women with other cancers (controls). The rate-ratio estimate (relative risk) for current smokers as compared with women who had never smoked was 0.7 (95 per cent confidence interval, 0.5 to 1.0), and for former smokers the estimate was 0.9 (0.6 to 1.2). For women currently smoking 25 or more cigarettes per day, the rate-ratio estimate was 0.5 (0.3 to 0.8). The effect of current smoking of at least 25 cigarettes per day appeared to be confined to postmenopausal women, among whom the estimate was 0.5 (0.2 to 0.9). Among premenopausal women the estimate was 0.9 (0.4 to 2.2), but the difference between these two estimates could have been due to chance. The data suggest that women who smoke heavily may have a lower risk of endometrial cancer than nonsmokers. The present findings do not have direct public health importance since cigarettes, overall, have serious deleterious effects. However, if these results are confirmed, elucidation of the underlying mechanisms whereby smoking reduces the risk would be of interest and might be useful in the development of strategies for preventing endometrial cancer.