After 12 years of screening for breast cancer in Nijmegen (1975-86), during which period six mammographic examination rounds were carried out, the extent of overdiagnosis was evaluated. Overdiagnosis is defined as a histologically established diagnosis of invasive or intraductal breast cancer that would never have developed into a clinically manifest tumour during the patient's normal life expectancy if no screening examination had been carried out. The whole 12-year period shows an excess of 11% of breast cancer cases in Nijmegen, compared with the neighbouring city of Arnhem, where no mass screening was performed. The incidence of breast cancers in Nijmegen in the period 1975-78 is higher, compared with the incidence rates in Arnhem; the rate ratio is 1.30. For the time-intervals 1979-82 and 1983-86 the rate ratios are 1.03 and 1.01 respectively with (0.89; 1.18) and (0.86; 1.16) as 95% confidence intervals. This leads to the conclusion that there is no evidence that screening programmes using modern mammography constitute a significant risk for overdiagnosis of breast cancers.
The etiology of middle ear disease in Nijmegen, The Netherlands was studied on the basis of a data set collected in a prospective epidemiological study on otitis media with effusion (OME) in a cohort of 1439 preschool children. A factor analysis was used to evaluate two hypotheses: (1) that OME, acute otitis media (AOM), common cold and tonsillitis are manifestations of the same pathological entity, and (2) that a group of children can be distinguished who develop these conditions more frequently than average. The results only partly supported these hypotheses. The correlation between OME, AOM, common cold and tonsillitis was lower than expected from a review of the literature. Common cold appeared to be the ubiquitous ENT disease in childhood and, depending on the child's predisposition, could be accompanied by OME, AOM or tonsillitis. The course of middle ear and upper airway disease showed a gradual scale from "healthy" to "ill" with most of the children suffering from these conditions at an average frequency.
Methods of analysing and presenting longitudinal data on health characteristics that have a fluctuating course are by no means standard. Several possibilities are discussed and tried out on longitudinal data on Otitis Media with Effusion (OME) in Dutch children. If the purpose of a study is descriptive, a graphical presentation based on an idea from Fiellau-Nikolajsen is preferred. For estimation purposes on the other hand, hazard functions are the most suitable. Further reduction of the data does not lead to a clear view into the complex nature of the course of a disease such as OME.
Recent case-referent studies in the Nijmegen breastscreening programme have shown a reduction in breastcancer mortality of approximately 50% due to screening of women aged 65 years and older. In this type of study, however, the results may be biased because of self-selection. The purpose of our present study was to compare the breast-cancer mortality rate in a population invited for screening with that of a reference population from an area without a screening programme. In 1977-1978, 6773 women aged 68-83 years were enrolled in the mammographic screening programme in Nijmegen, The Netherlands. The women were followed up until 31 December, 1990. The reference population consisted of women from the same birth cohort from Arnhem, a neighbouring city without mass screening, for whom the entry date was 1 January, 1978. The ratios of the Nijmegen and Arnhem breast-cancer mortality rates with 95% confidence intervals (CI) were calculated. In the study period, 173 patients were diagnosed with primary breast cancer in Nijmegen vs. 183 in Arnhem; 40 Nijmegen patients had died of breast cancer vs. 51 Arnhem patients. The cumulative mortality-rate ratio was 0.80 (95% CI 5 0.53-1.22). In the periods 1978-1981, 1982-1985 and 1986-1990, the mortality rate ratios were 1.44 (95% CI 5 0.67-3.10), 0.81 (95% CI 5 0.37-1.79) and 0.53 (95% CI 5 0.27-1.04), respectively. After adjustment for the difference in incidence rate that existed between the Nijmegen and Arnhem populations, mammographic screening of women older than 65 can be expected to yield a 40% reduction in breast-cancer mortality after 10 years. Int. J. Cancer, 70:164-168, 1997.r 1997 Wiley-Liss, Inc.Unlike most malignancies, the course of breast cancer can be altered by early detection and treatment. In women over the age of 50 years, trials have shown a reduction of breast-cancer mortality of some 25 to 30% in populations that were offered screening vs. unscreened populations (Fletcher et al., 1993; Nyström et al., 1993;De Koning et al., 1995;Kerlikowske et al., 1995). The screening intervals used in these studies ranged from 12 to 33 months and the screening test consisted of 1-or 2-view mammography, sometimes in combination with physical examination.More recently, a reduction in mortality has been demonstrated in women up to the age of 75 years (Van Dijck et al., 1994Chen et al., 1995). The results of the Swedish 2-county study, which was a randomized trial, showed a decrease in breast-cancer mortality due to the screening of women aged 65 to 74 years at entry (Chen et al., 1995). After 14 years of follow-up, a statistically significant 32% reduction in the risk of death from breast cancer was observed in the population invited for screening. In Nijmegen, 2 case-referent studies included women aged 65 years and older at the index invitation (i.e., the most recent invitation to screening just prior to the diagnosis of breast cancer in the case). The estimated reductions in breast-cancer mortality in women screened at the index invitation relative to those unscreened a...
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