"Alternative" controls in a case-control study of endometrial cancer and exogenous estrogen

Asthma and risk of glioma: a population-based case-control study

OBJECTIVES

Literature suggests an inconsistent, but largely inverse, association between asthma and risk of glioma, which is primarily due to methodological inconsistency in sampling frame and ascertainment of asthma. The objective of the study was to clarify the association between asthma and risk of glioma by minimising methodological biases (eg, recall and detection bias).

DESIGN

A population-based case-control study.

SETTING

General population in Olmsted County, Minnesota, USA.

PARTICIPANTS

All eligible biopsy-proven incident glioma cases (1995-2014) and two sets of controls among residents matched to age and sex (first set: community controls without glioma; second set: MRI-negative controls from the same community).

METHODS

The predetermined asthma criteria via medical record review were applied to ascertain asthma status of cases and controls. History of asthma prior to index date was compared between glioma cases and their matched controls using conditional logistic regression models. Propensity score for asthma status was adjusted for multivariate analysis.

RESULTS

We enrolled 135 glioma cases (median age at index date: 53 years) and 270 controls. Of the cases, 21 had a history of asthma (16%), compared with 36 of MRI controls (27%) (OR (95% CI) 0.48 (0.26 to 0.91), p=0.03). With MRI controls, an inverse association between asthma and risk of glioma persisted after adjusting for the propensity score for asthma status, but did not reach statistical significance probably due to the lack of statistical power (OR (95% CI) 0.48 (0.21 to 1.09); p=0.08). Based on comparison of characteristics of controls and cases, community controls seem to be more susceptible to a detection bias.

CONCLUSIONS

While differential detection might account for the association between asthma and risk of glioma, asthma may potentially pose a protective effect on risk of glioma. Our study results need to be replicated by a larger study.

Association of Endometrial Cancer Risk With Postmenopausal Bleeding in Women: A Systematic Review and Meta-analysis

IMPORTANCE

As the worldwide burden of endometrial cancer continues to rise, interest is growing in the evaluation of early detection and prevention strategies among women at increased risk. Focusing efforts on women with postmenopausal bleeding (PMB), a common symptom of endometrial cancer, may be a useful strategy; however, PMB is not specific for endometrial cancer and is often caused by benign conditions.

OBJECTIVE

To provide a reference of the prevalence of PMB in endometrial cancers and the risk of endometrial cancer in women with PMB.

DATA SOURCES

For this systematic review and meta-analysis, PubMed and Embase were searched for English-language studies published January 1, 1977, through January 31, 2017.

STUDY SELECTION

Observational studies reporting the prevalence of PMB in women with endometrial cancer and the risk of endometrial cancer in women with PMB in unselected populations were selected.

DATA EXTRACTION AND SYNTHESIS

Two independent reviewers evaluated study quality and risk of bias using items from the Newcastle-Ottawa Quality Assessment Scale and the Quality Assessment of Diagnostic Accuracy Studies tool. Studies that included highly selected populations, lacked detailed inclusion criteria, and/or included 25 or fewer women were excluded.

MAIN OUTCOMES AND MEASURES

The pooled prevalence of PMB in women with endometrial cancer and the risk of endometrial cancer in women with PMB.

RESULTS

A total of 129 unique studies, including 34 432 unique patients with PMB and 6358 with endometrial cancer (40 790 women), were analyzed. The pooled prevalence of PMB among women with endometrial cancer was 91% (95% CI, 87%-93%), irrespective of tumor stage. The pooled risk of endometrial cancer among women with PMB was 9% (95% CI, 8%-11%), with estimates varying by use of hormone therapy (range, 7% [95% CI, 6%-9%] to 12% [95% CI, 9%-15%]; P < .001 for heterogeneity) and geographic region (range, 5% [95% CI, 3%-11%] in North America to 13% [95% CI, 9%-19%] in Western Europe; P = .09 for heterogeneity).

CONCLUSIONS AND RELEVANCE

Early detection strategies focused on women with PMB have the potential to capture as many as 90% of endometrial cancers; however, most women with PMB will not be diagnosed with endometrial cancer. These results can aid in the assessment of the potential clinical value of new early detection markers and clinical management strategies for endometrial cancer and will help to inform clinical and epidemiologic risk prediction models to support decision making.

Diet and Melanoma Risk: Effects of Choice of Hospital versus Population Controls

Aims and background

Hospital-referred subjects are widely used as controls in studies on the relation between diet and cancer risk. However, concern has been raised about the potential for bias of such type of referents, and few studies seem to have examined their reliability in estimating dietary habits of the underlying general population.

Methods

In a northern Italian setting, the differences in dietary patterns between 41 individuals referred for non-neoplastic lesions to hospital surgical outpatient units and age- and sex-matched subjects drawn from the general population were examined. The effects of such differences when carrying out a case-control study on a neoplastic disease, cutaneous melanoma, were also analyzed. Dietary intake was assessed using the EPIC food frequency questionnaire.

Results

Population controls showed higher intakes of energy, animal proteins and animal fats compared with sex- and age-matched hospital controls, whereas intake of carbohydrates and fiber was comparable. An excess melanoma risk associated with intake of animal proteins and fats emerged when hospital controls were used as the referent group, whereas no such relation was detected when cases were compared to population controls.

Conclusions

The results suggest that hospital-referred subjects may not reflect dietary habits of the underlying general population and may be unsuitable for case-control studies concerning the relation between diet and cancer risk.

Comparative study of control selection in a national population-based case-control study: Estimating risk of smoking on cancer deaths in Chinese men

PURPOSE

To assess the validation of a novel control selection design by comparing the consistency between the new design and a routine design in a large case-control study that was incorporated into a nationwide mortality survey in China.

METHODS

A nationwide mortality study was conducted during 1989-1991. Surviving spouses or other relatives of all adults who died during 1986-1988 provided detailed information about their own as well as the deceased person's smoking history. In this study, 130,079 males who died of various smoking-related cancers at age 35 or over were taken as cases, while 103,248 male surviving spouses (same age range with cases) of women who died during the same period and 49,331 males who died from causes other than those related to smoking were used as control group 1 and control group 2, respectively. Consistency in the results when comparing cases with each of the control groups was assessed.

RESULTS

Consistency in the results was observed in the analyses using different control groups although cancer deaths varied with region and age. Equivalence could be ascertained using a 15% criterion in most cancer deaths which had high death rates in urban areas, but they were uncertain for most cancers in rural areas irrespective of whether the hypothesis testing showed significant differences or not.

CONCLUSIONS

Sex-matched living spouse control design as an alternative control selection for a case-control study is valid and feasible, and the basic principles of the equivalence study are also supported by epidemiological survey data.

Childbearing and mortality from cancer of the corpus uteri

BACKGROUND

To investigate the mortality from cancer of the corpus uteri in relation to parity and age at first and last birth.

METHODS

A cohort of 431,604 married women aged 45-74 years at the Norwegian Census in 1970 was followed over 15 years. A total of 752 deaths from cancer of the corpus uteri were diagnosed during follow-up.

RESULTS

All age groups showed significant trends of decreasing mortality rates with increasing number of children. The age-adjusted reduction in mortality was 9.2% (95% CI 5.2-13.0) for each child. Women with 8-11 children had a relative risk of 0.35 (95% CI 0.14-0.85) compared to nulliparous women. For first birth at age > = 35 years versus < = 19 years, the relative risk was 0.53 (95% CI 0.34-0.83). No significant effect of age at last birth was found.

CONCLUSIONS

This study supports the notion that high parity and postponing the first delivery may reduce the risk of uterine cancer death.

Endometrial cancer risk after discontinuing use of unopposed conjugated estrogens (California, United States)

To examine the decline in risk of endometrial cancer after discontinuation of use of conjugated estrogens, we conducted a case-control study in a prepaid health plan. We identified 318 patients who had endometrial cancer but had no history of bilateral oophorectomy and had been in the Southern California (United States) Kaiser Foundation Health Plan for more than 10 years. For each patient, one or two control members were selected, 599 in all, matched for age and duration of membership at the time of cancer detection and who had had neither hysterectomy nor bilateral oophorectomy. A history of prescriptions for conjugated estrogens and of potential confounders was obtained for each subject by reviewing outpatient medical records. Rate ratios (RR) contrasting users with nonusers were estimated by time of latest prescription. We found that estrogen-induced risk of endometrial cancer decreases rapidly as the estrogen-free interval increases. The RR estimates, adjusted for duration of use and potential confounding factors, declined from 5.0 for those receiving their latest prescription within 24 months (95 percent confidence limits [CL] = 2.6-9.8), to 1.8 for those receiving their latest prescription within 24 to 48 months (CL = 0.9-3.7), to values near one for each latest prescription interval earlier than 48 months ago (P for trend = 0.00004). For those who used conjugated estrogens extensively (five or more prescriptions, five to 10 years ago), the RR estimate declined from 5.1 for those whose latest prescription was within two years to 0.6 yr for those whose latest prescription was four to five years previously (P for trend = 0.05).

Selection of neighborhood controls for a study of factors related to the diagnosis of cervical cancer

The level of effort required to generate neighborhood controls for a statewide matched case-control study of cervical cancer was investigated, with the aim of identifying hard-to-reach demographic subgroups. Cross reference telephone directories were used to identify households on the same street as the case. Letters were then sent to the households, followed by 'phone calls. A total of 2920 households were contacted to obtain 147 controls. Overall, 63.6% of age-eligible contacts participated in the study. In 49.3% of all households the major reason for not obtaining a control was "no age-eligible women". Level of effort required to obtain a matched control was greater for black women than for white women--on average 24 letters and 40 'phone calls for black women vs 12 letters and 20 calls for white women. Fewer eligible younger women refused to be interviewed than older. No marked differences were noted when the data were stratified by urban-rural area of residence.

Postmenopausal unopposed estrogens. Characteristics of use in relation to the risk of endometrial carcinoma

To determine whether treatment regimens for unopposed estrogens can be tailored so as to minimize the excess risk of endometrial cancer, results from 19 published studies of the association between unopposed estrogen use and endometrial cancer were compiled. We sought to examine the influence of duration of use, recency, dose, type of estrogen preparation, and periodic interruption of use on cancer incidence. Estrogen use for 5 years or longer was examined in 18 studies and was associated with a large increase in the risk of endometrial cancer in each one (range in relative risk, 1.8 to 36). Use for shorter durations also was observed to increase risk; however, among women who used estrogens for less than 6 months, any increased risk that may exist appears to be very small in size (six studies; range, 0.6 to 1.4). Risk consistently was seen to decrease with increasing time since cessation of use, although there is evidence from seven of eight studies that some residual excess risk remains long after estrogens have been discontinued. In each of 12 studies that examined the influence of dose, all dose levels of conjugated estrogens increased risk of endometrial cancer substantially. Four of five studies found no differences between oral synthetic estrogens and conjugated estrogens with respect to cancer risk, and all of eight studies found no difference between cyclic and continuous regimens. Based on our review, we conclude that apart from minimizing the duration of use, there is no way of taking unopposed postmenopausal estrogens that reduces their potential to cause endometrial cancer.

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.

Reproductive factors and cancers of the breast, ovary and endometrium

In contrast to cancers of non-hormone-dependent sites, cancers of the breast, ovary and endometrium show a slowing down of the rate of increase in incidence at around age 50, as if ceasing menstrual activity reduced risk. Also nulliparous women appear more prone to these three cancers as compared to parous women, thus suggesting that pregnancies also represent a 'protected' time. Epidemiological studies on breast cancer, the only ones sufficiently large to try to disentangle meaningfully the effects of collinear reproductive variables such as parity and ages at first and last birth, show, however, that the effect of pregnancy is not simple and depends on how many births take place and at what age. Larger population-based investigations able to obtain with greater precision information not only on reproductive factors but also on possible confounding variables (e.g. socio-economic status, dietary habits, etc.) are mandatory, particularly as regards ovarian cancer and endometrial cancer. The lesson from the recent studies on pregnancy-related events and breast cancer is, however, that initially a decrease of old certainties must be expected to derive from the accumulation of new, better epidemiological data.

Risk factors of female cancers in Ragusa population (Sicily)--1. Endometrium and cervix uteri cancers

A case-control study on breast, cervix and endometrium cancer cases registered in Ragusa between January 1, 1983 and June 30, 1985 has been conducted. Information on risk factors has been obtained by means of a structured questionnaire. Risk factors for endometrium cancer were: few children (1-2 vs greater than 4 OR 15.18, 95%CL 1.96-117.64), oestrogenic treatment (OR 2.20, 95%CL 1.05-4.90), obesity (Quetelet index greater than 30 vs less than 22 OR 10.42, 95%CL 1.30-83.86), family history (OR 2.87, 95% CL 1.05-7.83). Risk factors for cervix uteri cancer were: multiple abortions (greater than 2 vs 0 OR 9.87, 95%CL 1.46-66.66), no contraception (OR 8.33, 95%CL 2.38-25.00), younger age of mother at birth (OR 6.89, 95%CL 1.71-27.70). Age at menarche, age at menopause and years of fertile life were not found to be related to either endometrium or cervix uteri cancer. The existence of influencing differences (ancestry, environment, lifestyle) has been postulated.

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.

Alcohol consumption and risk of benign proliferative epithelial disorders of the breast in women

Many studies have shown a positive association between alcohol consumption and risk of breast cancer. Benign proliferative epithelial disorders (BPED) of the breast are conditions which, although not proven precursors of breast cancer, are strongly associated with increased risk of this disease. The association between alcohol consumption and risk of BPED was examined in a case-control study conducted in Adelaide, South Australia. The study involved 383 cases with biopsy-confirmed BPED, 192 controls whose biopsy did not show epithelial proliferation, and 383 unbiopsied community controls individually matched (I:I) to cases on age and area of residence. When cases were compared with community controls, the unadjusted relative risk of BPED for drinkers versus non-drinkers was 0.9 (95% CI 0.6-1.3), and the corresponding relative risk derived from comparing cases with biopsy controls was 1.0 (95% CI 0.6-1.4); these estimates were not altered after adjustment for potential confounding. Variation in risk of BPED across levels defined in terms of daily total alcohol intake, and in terms of daily alcohol intake from individual beverages, was mostly insubstantial and not dose-dependent. Also, there was little variation in risk with age at first drink, or by current drinking status, and risk of BPED in association with alcohol consumption did not increase with severity of cytologic atypia. Despite the absence of an association in this study, further investigation is warranted, since it may provide opportunities for the prevention of BPED and of breast cancer.

Simultaneous interval estimates of the odds ratio in studies with two or more comparisons

More than one odds ratio estimate will often arise from a single epidemiologic study. Examples of designs where this may occur include those where there is more than one case or control group, and investigations of several risk factors as part of the same study. Various methods for presenting multiple interval estimates are discussed, including: the naive method, the Bonferroni method, the Dunn method, the Scheffé method, and the Dunnett method. For rectangular regions the Dunnett method gives a region with the most appropriate confidence level, but this region contains a different set of odds ratio estimates than are implied by the usual significance tests. A confidence ellipse circumscribed by the Scheffé limits gives the best agreement with the significance tests. Each of these methods is illustrated with a numerical example.

CYTO-Histologic Evaluation of the Endometrium in Climacteric Women at Risk for Endometrial Carcinoma

The authors evaluated the diagnostic effectiveness of a triple specimen technique (cyto-histologic) performed by the Perma device. The incidence of endometrial hyperplasia (according to Dallenbach-Hellweg's classification) was estimated in 254 climacteric women selected from outpatients who come spontaneously to the Menopause Clinic of the Obstetrics and Gynecology Department (Bologna University). The selection criterion was the evidence of risk factors for endometrial carcinoma, climacteric bleedings (obesity, late menopause, high blood pressure, diabetes), or endometriotropic estrogen therapy in the postmenopause. Results showed that the cyto-histologic sampling is most useful for diagnosing endometrial hyperplasia and early carcinoma (diagnostic effectiveness: 89.0-93.8%). Also, endometrial hyperplasia was found to have a significant incidence in the group we examined. This incidence was highest in women with climacteric bleedings, secondly in women using high-dose estrogens, and thirdly in women with risk factors for endometrial carcinoma. When evaluating the different kinds of endometrial hyperplasia, we never found adenomatous hyperplasia in women on estrogen therapy. Affinity between histologic and cytologic classes was around 50% in endometrial hyperplasia and 100% in early carcinoma. This emphasizes that both samplings are needed to perform an accurate diagnosis.

Endometrial carcinogenesis and its relation to oestrogens

The epidemiological evidence suggesting an association between the administration of exogenous oestrogens and an increased risk of developing endometrial adenocarcinoma is critically reviewed and it is concluded that the case for oestrogens being a cause of endometrial cancer is proven. The benefits flowing from preventing postmenopausal osteoporosis by oestrogen replacement therapy are assessed and contrasted with the danger to life posed by endometrial adenocarcinoma: it is pointed out that the type of neoplasm developing in patients taking oestrogens is well differentiated, nonaggressive and easily cured, the survival rate being very high. The addition of progestational agents to the therapeutic regime may prevent the development of endometrial carcinoma but could introduce a risk of cardiovascular disease.

Comparison of megestrol acetate and clomiphene citrate as supplemental medication in postmenopausal oestrogen replacement therapy

In a prospective clinical trial lasting one year, 35 postmenopausal women with severe climacteric symptoms were cyclically treated with conjugated oestrogens (1.25 mg daily). This oestrogen replacement therapy was randomly supplemented with 10 mg of megestrol acetate daily (18 women) or 50 mg of clomiphene citrate (17 women) for 10 days four times a year. Both treatment regimens significantly alleviated climacteric symptoms. At the end of the oestrogen-megestrol acetate treatment no endometrial proliferation or hyperplasia was seen, while at the end of the oestrogen-clomiphene citrate treatment the endometrium was proliferative or hyperplastic in two women and atrophic in the other 15. Regular uterine bleeding occurred in each woman after megestrol acetate but never after clomiphene citrate administration. Break-through bleeding during the oestrogen treatment periods appeared in the megestrol and clomiphene groups in five and eight women, respectively. There were no clinically adverse hormonal or metabolic changes during megestrol acetate or clomiphene citrate treatment periods. Our results provide further evidence that in addition to progestins postmenopausal oestrogen replacement therapy can safely be supplemented with antioestrogen and thereby avoid the bleeding which occurs regularly after progestin withdrawal.

Cautions on the use of medical databases

The use of medical databases is tied in with the conduct of epidemiologic and clinical investigations. I expound the thesis that investigative results are frequently ambiguous and subject to a multiplicity of interpretations, some even diametrically opposed, and describe examples of such situations. For instance, the very fact that an agent is particularly safe may make it seem dangerous--the agent becomes the one of choice for high risk patients. Other topics include the use of models, including regression models, Cox's proportional hazard model, the search for epidemiologic interactions, ratio measures, and grouping effects.

Hormones, medications, and cancer

Hormones have been shown experimentally to act as cocarcinogens or promoters, i.e., they facilitate the carcinogenic event. In the cases of breast and endometrium, those hormones that facilitate growth may also favor carcinogenesis in the human. There is good epidemiologic evidence that use of estrogens after the menopause increases the incidence of breast and endometrial cancer, the risk increasing with increasing duration of use. Periodic progestin-induced withdrawal will probably mitigate the risk of endometrial cancer after the menopause. Prolactin is the important promoter of mammary cancer in the rat and mouse, but its significance in women is still under study. Intermittently elevated prolactin levels have been noted in some women who subsequently developed breast cancer, but epidemiologic studies of women who have received prolactin-releasing drugs such as reserpine and perphenazine have not disclosed increased risk. Diethylstilbestrol is listed as a carcinogen but any estrogen can induce mammary cancer in the rodent or vaginal adenosis in the neonatal mouse (an experimental model of human vaginal adenocarcinoma).