The results of the Swedish Two-County Trial of mammographic screening are qualitatively the same at 29-year follow-up as when they were first published: A substantial and significant reduction in breast cancer mortality was associated with an invitation to screening. PurposeTo estimate the long-term (29-year) effect of mammographic screening on breast cancer mortality in terms of both relative and absolute effects.Materials and MethodsThis study was carried out under the auspices of the Swedish National Board of Health and Welfare. The board determined that, because randomization was at a community level and was to invitation to screening, informed verbal consent could be given by the participants when they attended the screening examination. A total of 133 065 women aged 40–74 years residing in two Swedish counties were randomized into a group invited to mammographic screening and a control group receiving usual care. Case status and cause of death were determined by the local trial end point committees and, independently, by an external committee. Mortality analysis was performed by using negative binomial regression.ResultsThere was a highly significant reduction in breast cancer mortality in women invited to screening according to both local end point committee da...

Background. Several studies have found a smaller effect of breast cancer screening on breast cancer mortality in women aged younger than 50 years compared with older women. Various possible reasons have been suggested for this, but none firmly is established. Methods. The Swedish Two‐County Study is a randomized trial of breast cancer screening of women aged 40‐74 years, comprising with 133,065 women with a 13‐year follow‐up of 2467 cancers. The Breast Cancer Detection Demonstration Project (BCDDP) is a nonrandomized screening program in the United States, with a 14‐year follow‐up of 3778 cancers in women aged 40‐74 years. The Swedish results by age were updated. The lesser effect of screening at ages 40‐49 years was investigated in terms of sojourn time (the duration of the preclinical but detectable phase) size, lymph node status, and histologic type of the tumors diagnosed in the Swedish Study and their subsequent effect on survival using survival data from both studies. Results. In the Swedish Trial, a 30% reduction in mortality associated with the invitation to screening of women aged 40‐74 years was maintained after 13‐years of follow‐up. The reduction was 34% for women aged 50‐74 years and 13% for women aged 40‐49 years. Results indicated that the reduced effect on mortality for women aged 40‐49 years was due to a differential effect of screening on the prognostic factors of tumor size, lymph node status, and histologic type. The mean sojourn times in the age groups 40‐49 years, 50‐59 years, 60‐69 years, and 70‐74 years were 1.7,3.3,3.8, and 2.6 years, respectively. Conclusions. These results suggest that much, a though not all, of the smaller effect of screening on mo tality in women aged 40‐49 years is due to faster progression of a substantial proportion of tumors in this age group and the rapid increase in incidence during this decade of life. It is concluded that the interval between screenings should be shortened to achieve a greater benefit in this age group. It is estimated that a 19% reduction in mortality would result from an annual screening regime.

Background: It is of paramount importance to evaluate the impact of participation in organized mammography service screening independently from changes in breast cancer treatment. This can be done by measuring the incidence of fatal breast cancer, which is based on the date of diagnosis and not on the date of death. Methods: Among 549,091 women, covering approximately 30% of the Swedish screening‐eligible population, the authors calculated the incidence rates of 2473 breast cancers that were fatal within 10 years after diagnosis and the incidence rates of 9737 advanced breast cancers. Data regarding each breast cancer diagnosis and the cause and date of death of each breast cancer case were gathered from national Swedish registries. Tumor characteristics were collected from regional cancer centers. Aggregated data concerning invitation and participation were provided by Sectra Medical Systems AB. Incidence rates were analyzed using Poisson regression. Results: Women who participated in mammography screening had a statistically significant 41% reduction in their risk of dying of breast cancer within 10 years (relative risk, 0.59; 95% CI, 0.51‐0.68 [ P < .001]) and a 25% reduction in the rate of advanced breast cancers (relative risk, 0.75; 95% CI, 0.66‐0.84 [ P < .001]). Conclusions: Substantial reductions in the incidence rate of breast cancers that were fatal within 10 years after diagnosis and in the advanced breast cancer rate were found in this contemporaneous comparison of women participating versus those not participating in screening. These benefits appeared to be independent of recent changes in treatment regimens.

BACKGROUND: The evaluation of organized mammographic service screening programs is a major challenge in public health. In particular, there is a need to evaluate the effect of the screening program on the mortality of breast carcinoma, uncontaminated in the screening epoch by mortality from 1) cases diagnosed in the prescreening period and 2) cases diagnosed among unscreened women (i.e., nonattenders) after the initiation of organized screening.METHODS: In the current study, the authors ascertained breast carcinoma deaths in the prescreening and screening epochs in 7 Swedish counties from tumors diagnosed in these epochs and in the age group 40–69 years in 6 counties and 50–69 years in 1 county. Data regarding deaths were obtained from the Uppsala Regional Oncologic Center in conjunction with the National Cause of Death Register. The total number of women in the eligible age range living in each county was obtained from the annual population data of Statistics Sweden. Detailed screening data were provided by the screening centers in the seven counties, including the number of invited, the number attended, and whether each individual breast carcinoma case was exposed (screen‐detected and interval cases combined) or unexposed (not‐invited or nonattenders) to mammographic screening. There were 2044 breast carcinoma deaths from 14,092 incident tumors diagnosed in the prescreening and screening epochs, and the total number of person‐years was 7.5 million. Data were analyzed using Poisson regression with corrections for self‐selection bias and lead‐time bias when appropriate.RESULTS: The mortality reduction for breast carcinoma in all 7 counties combined for women actually exposed to screening compared with the prescreening period was 44% (relative risk [RR] = 0.56; 95% confidence interval [95% CI], 0.50–0.62). When all incident tumors were considered, both those exposed and those unexposed to screening combined, counties with > 10 years of screening were found to demonstrate a significant 32% mortality reduction (RR = 0.68; 95% CI, 0.60–0.77) and counties with ≤ 10 years of screening showed a significant 18% reduction in breast carcinoma mortality (RR = 0.82; 95% CI, 0.72–0.94) for the screening epoch compared with the prescreening epoch. Within the screening epoch, after adjustment for self‐selection bias, a 39% mortality reduction (RR = 0.61; 95%CI, 0.55–0.68) was observed in association with invitation to screening.CONCLUSIONS: Organized service screening in 7 Swedish counties, covering approximately 33% of the population of Sweden, resulted in a 40–45% reduction in breast carcinoma mortality among women actually screened. The policy of offering screening is associated with a mortality reduction in breast carcinoma of 30% in the invited population, exposed and unexposed combined. The results of the current study indicate that the majority of the breast carcinoma mortality reduction is indeed due to the screening. [See editorial on pages 451–7, this issue.] Cancer 2002;95:458–69. © 2002 American Cancer Society.DOI 10.1002/cncr.10765