An historical cohort study of cardiac catheterization during childhood and the risk of cancer.

This study aimed to determine whether cancer risk was elevated among patients exposed to radiation from diagnostic cardiac catheterization during childhood. The study cohort included 3915 children who underwent at least one cardiac catheterization at a major children's hospital in Toronto, Canada, between 1950 and 1965, were < or = 18 years at the time of the procedure, and were residents of Ontario. Follow-up of the cohort was done by linkage to the Ontario Cancer Registry up to 1986. A total of seven cancer deaths were observed (O), compared with 5.7 expected (E) based on provincial cancer rates (mortality ratio [O/E] = 1.2; 90% confidence interval [CI] : 0.6-2.3). In the analysis of cancer incidence, 13 cancers were detected, compared with 17.3 expected (O/E = 0.75; 90% CI : 0.4-1.2). These mortality and incidence ratios were not statistically significantly elevated. Detailed analyses were conducted according to age at exposure, age at diagnosis, sex, number of procedures, year of first catheterization, and latent period. Detected deviations in risk were confined to an early period of exposure, indicating that later practices of cardiac catheterization were not associated with increased risk. In general, there was no statistically significant excess risk of cancer among the cohort.

Risk factors for renal cell carcinoma: results of a population-based case-control study.

For a case-control study of risk factors for renal cell carcinoma, a mailed questionnaire was used to collect data on 518 cases and 1,381 population-based controls in Ontario, Canada. Active cigarette smoking increased risk twofold among males (odds ratio estimate [OR] = 2.0, 95 percent confidence interval (CI) = 1.4-2.8) and females (OR = 1.9, CI = 1.3-2.6). Passive smoking appeared to increase risk somewhat among nonsmokers (males: OR = 1.6, CI = 0.5-4.7; females: OR = 1.7, CI = 0.8-3.4). A high Quetelet index (QI) was associated with a twofold increase in risk in both sexes, although this was based on reported weight at age 25 years for males (OR = 1.9, CI = 1.2-3.1) and five years prior to data collection for females (OR = 2.5, CI = 1.4-4.6). Diuretic use was associated with significantly increased risk among females, but not among males. Phenacetin use increased risk, while acetaminophen use was not associated with altered risk, although few subjects used either compound. Multiple urinary tract infections increased risk, but only significantly in females (OR = 1.9, CI = 1.2-2.9). Our data indicate the need for further exploration of passive smoking and diuretics as risk factors, as well as elucidation of mechanisms by which high lifetime QI and frequent urinary-tract infections might increase risk of this cancer.

The effect on response rates of offering a small incentive with a mailed questionnaire.

To determine whether response rates to a mailed questionnaire sent to population control subjects could be increased through offer of a small incentive, half of the control subjects (n = 477) in a case-control study of renal cell carcinoma were randomly selected to receive a contact letter offering a lottery ticket if a completed questionnaire was returned; the remaining subjects (n = 477) received the same letter but with no mention of a lottery ticket. Overall response rates did not differ between the two groups (72.6% versus 74.4%), although a higher percentage of those offered a lottery ticket responded without follow-up (24.4% versus 18.5%). Binomial regression modeling of the effect of the lottery ticket offer, sex, age, and percent of urban dwellers on response indicated a significant effect only for percent of urban dwellers, the rate of response increasing with a decreasing percentage of urban dwellers. The effect of sex was of borderline significance (P = 0.05), with females having the higher rate of response.

Risk factors for adenomatous endometrial hyperplasia: a case-control study.

A population-based case-control study of histologically confirmed endometrial neoplasia was conducted in Toronto, Canada, between 1977 and 1978. Pathologic slide review resulted in classification of patients to diagnostic categories of endometrial carcinoma, endometrial carcinoma in situ, and endometrial hyperplasia. This report concerns the subset of patients classified as having adenomatous endometrial hyperplasia. Two age-matched neighborhood controls were selected for each case, and analyses included only those case-control sets in which the case and at least one control were concordant on menopausal status. Among postmenopausal women (87 cases and 151 controls), noncontraceptive estrogen use was a statistically significant risk factor (adjusted odds ratio (OR) = 6.7), as was heavy body weight relative to height (Quetelet index) (adjusted OR = 3.2). Long-term (5+ years) estrogen use conferred an estimated relative risk of more than 20, but use of oral contraceptives did not alter risk significantly. Among premenopausal women (62 cases and 97 controls), a high Quetelet index appeared to be a significant protective factor, even when adjusted for oral contraceptive use (adjusted OR = 0.2). While oral contraceptive use was not associated with a change in risk, long duration of use was highly, but statistically not significantly, protective against hyperplasia. The data for pre- and postmenopausal women indicate that both endogenous and exogenous estrogen exposure are important factors in the etiology of adenomatous endometrial hyperplasia.

Optimal frequency of screening for cervical cancer: a Toronto case-control study.

A retrospective (case-control) study was conducted in Toronto, Canada, between 1973 and 1976 to evaluate the effectiveness of the Papanicolaou smear as a screening procedure for invasive carcinoma of the cervix. In the current study, data from cases of squamous cell cancer of the cervix and controls without hysterectomy were analysed to assess the optimal frequency of cervical screening. The time between the last normal smear and the date of diagnosis was divided into 12-month intervals. Relative protections were then calculated by comparing women who had had one or more normal smears with those who had never been screened. The results show a significant protective effect of screening in women who have had two or more normal smears, when the last was taken within two years of diagnosis. This trend, although not statistically significant, continued even when the last was taken four years before diagnosis, suggesting that screening intervals should not be greater than four years.

Problems in determining the incidence of cervical cancer.

Since cancer registries have different recording practices, the incidence rates that they report must be compared with caution. Indexes of reliability of recording indicated that in 1971 the reported incidence of cervical cancer in Ontario was too high. In 1971 Ontario used a method of passive reporting of cancer cases: the Ontario Cancer Registry linked hospital reports, death certificates and reports from the Ontario Cancer Treatment and Research Foundation's treatment centres to produce a single record for each case. Pathological confirmation was requested for cases thus recorded by the registry. In 26% of cases a diagnosis other than cervical cancer was indicated. With these cases omitted, the incidence rate became 15.1/100 000, as opposed to the 20.5/100 000 reported by the registry.