Early detection of breast cancer rectifies inequality of breast cancer outcomes.

OBJECTIVES: To explain apparent differences among mammography screening services in Sweden using individual data on participation in screening and with breast cancer-specific survival as an outcome. METHODS: We analysed breast cancer survival data from the Swedish Cancer Register on breast cancer cases from nine Swedish counties diagnosed in women eligible for screening. Data were available on 38,278 breast cancers diagnosed and 4312 breast cancer deaths. Survival to death from breast cancer was estimated using the Kaplan-Meier estimate, for all cases in each county, and separately for cases of women participating and not participating in their last invitation to screening. Formal statistical comparisons of survival were made using proportional hazards regression. RESULTS: All counties showed a reduction in the hazard of breast cancer death with participation in screening, but the reductions for individual counties varied substantially, ranging from 51% (95% confidence interval 46-55%) to 81% (95% confidence interval 74-85%). Survival rates in nonparticipating women ranged from 53% (95% confidence interval 40-65%) to 74% (95% confidence interval 72-77%), while the corresponding survival in women participating in screening varied from 80% (95% confidence interval 77-84%) to 86% (95% confidence interval 83-88%), a considerably narrower range. CONCLUSIONS: Differences among counties in the effect of screening on breast cancer outcomes were mainly due to variation in survival in women not participating in screening. Screening conferred similarly high survival rates in all counties. This indicates that the performance of screening services was similar across counties and that detection and treatment of breast cancer in early-stage reduces inequalities in breast cancer outcome.

Mammography screening reduces rates of advanced and fatal breast cancers: Results in 549,091 women.

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.

Service screening with mammography in Northern Sweden: effects on breast cancer mortality - an update.

OBJECTIVES: To study the effectiveness of service screening with mammography in Northern Sweden. SETTING: Two counties which invited women aged 40-74 years to service screening with mammography were compared with two counties where service screening started 5-7 years later. There were 109,000 and 77,000 women in the study and control counties, respectively. METHODS: Cohorts in the study group were defined to include only breast cancer cases diagnosed after their first invitation to screening. Two outcome measures for breast cancer mortality were used; excess mortality and underlying cause of death (UCD). Detection mode was used to estimate the efficacy of screening for those women who actually attended screening. The cohorts were followed for 11 years. RESULTS: The relative rate (RR) of breast cancer death as excess mortality and UCD for women aged 40-74 years invited to screening, compared with women not yet invited, was 0.70 (95% confidence interval [CI] 0.56-0.87) and 0.74 (95% CI 0.62-0.88), respectively. The largest effect was seen in women aged 40-49 years (RR = 0.64 and RR = 0.62 for excess mortality and UCD, respectively). RR in age 40-74 years for women actually screened was 0.65 (95% CI 0.51-0.84) and 0.70 (95% CI 0.57-0.86) for excess mortality and UCD, respectively. The number of women needed to screen to save one life was 912 after 11 years of follow-up. CONCLUSIONS: This study confirms previous findings in the earlier follow-up and indicates a long-term reduction of breast cancer mortality by 26-30%. The efficacy among those who actually attended screening was about 5% larger.