Effect of organized mammography screening on breast cancer mortality: A population-based cohort study in Norway.

We aimed to estimate the effect of organized mammography screening on incidence-based breast cancer mortality by comparing changes in mortality among women eligible for screening to concurrent changes in younger and older ineligible women. In a county-wise balanced, open-cohort study, we used birth cohorts (1896-1982) to construct three age groups in both the historical and screening period: women eligible for screening, and younger or older women ineligible for screening. We included women diagnosed with breast cancer who died within the same age-period group during 1987-2010 (n = 4,903). We estimated relative incidence-based mortality rate ratios (relative MRR) comparing temporal changes in eligible women to concurrent changes in ineligible women. Additionally, we conducted analyses comparing the change in eligible women to younger, ineligible women with either continued accrual and follow-up period (eligible women only) or continued follow-up period. All three age groups experienced a reduction in mortality, but the decrease among eligible women was about the same among ineligible women (relative MRR = 1.05, 95% CI: (0.94-1.18)). Varying the definition of follow-up yielded similar results. Mammography screening was not associated with a larger breast cancer mortality reduction in women eligible relative to ineligible women.

The Screening Illustrator: separating the effects of lead-time and overdiagnosis in mammography screening.

Background: Mammography screening increases incidence because cancers are detected earlier in time and because of overdiagnosis. We developed an Excel-based model to visualize the expected increase from lead-time amplified by increasing background incidence. Subsequently, we added overdiagnosis to the model. Methods: We constructed two hypothetical populations of women aged 50-79 in 5-year age and calendar groups: one with screening for women aged 50-69 and one without. The user enters information on population at risk, number of breast cancers, trends in background incidence, average length of lead-time and, optionally, overdiagnosis. The model computes incidence rate ratios (IRRs) comparing incidence changes with screening to changes without in open and closed cohorts. Results: We entered information from Norway from 1990 to 1994, the period preceding the gradual introduction of a national mammography screening programme. As expected, the Screening Illustrator showed prevalence peaks and compensatory drops. Only the closed cohort approach remained unaffected by increasing background incidence. The model showed a 20% sustained increase in incidence (IRR: 1.20) from lead-time and increasing background incidence in the open cohort approach for women aged 50-69. However, real life Norwegian data show a corresponding 38% increase. For the model to achieve the observed incidence, 10-14% overdiagnosis had to be added. Conclusion: The observed breast cancer incidence increase in Norway after screening implementation could not be obtained from an average lead-time of 2.5 years and empirical background incidence trends, but had to incorporate overdiagnosis.

Trends in stage-specific incidence of prostate cancer in Norway, 1980-2010: a population-based study.

OBJECTIVE: To estimate changes in the stage distribution of prostate cancer during the time period where opportunistic prostate-specific antigen (PSA) testing was introduced. PATIENTS AND METHODS: Cancer stage, age, and year of diagnosis were obtained for all men aged >50 years diagnosed with prostate cancer in Norway during the period 1980-2010. Three calendar-time periods (1980-1989, 1990-2000, and 2001-2010) and three age groups (50-65, 66-74, and ≥75 years) were defined. Birth cohorts were categorised into four intervals: ≤1915, 1916-1925, 1926-1940 and ≥1941. We used Poisson regressions to conduct both a time period and cohort-based analysis of trends in the incidence of localised, regional, and distant cancer for each combination of age groups and calendar-time periods or birth cohorts, respectively. Additionally, we explored the effect of cohorts on the stage-specific incidence graphically with a Poisson regression using 5-year age groups, and by estimating cumulative incidence rates for each birth cohort. RESULTS: The annual incidence of localised cancers among men aged 50-65 and 66-74 years rose from 41.4 and 255.2 per 100 000, respectively, before the introduction of PSA testing to 137.9 and 418.7 in 2001-2010 afterwards, corresponding to 3.3 [95% confidence interval (CI) 3.1-3.5] and 1.6 (95% CI 1.6-1.7) fold increases. The incidence of regional cancers increased by a factor seven among men aged <75 years. The incidence of distant cancers in men aged ≥75 years decreased by 29% (95% CI 25-33%). These findings were confirmed in the cohort-based approach. CONCLUSION: Opportunistic PSA testing substantially increased the incidence of localised and regional prostate cancers among men aged 50-74 years, which was not fully compensated by the 30% decrease in incidence of distant prostate cancers in older men.