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MAMMOGRAFI-Evaluering av Mammografiprogr

Research-based evaluation of the Norwegian mammography screening program; effectiveness, side-effects, and cost-effectiveness

Tildelt: kr 1,1 mill.

In Norway, more women have received a diagnosis of breast cancer each year, since the early 90ties. This is partly explained by the use of hormone replacement therapy (HRT) and mammography screening. Population screening in The Norwegian Breast Cancer Screening Programme (NBCSP) was gradually implemented from 1996 and covered the entire country in 2005. The aim of our study is to understand trends in breast cancer incidence and breast cancer mortality and to estimate the amount of overdiagnosis. Overdiagnosis occurs when women receive a diagnosis of breast cancer because of screening, while if they not had been screened would have never known that they had breast cancer. In most cases these women will undergo unnecessary treatment, this is called overtreatment. The third aim of this study is to investigate whether the NBCSP is cost-effective. A health intervention is considered cost-effective when the costs of the intervention per life year gained do not exceed an internationally agreed upon threshold. By using a computer simulation model, we could investigate the influence of mammography in the screening programme and outside the programme, and the use of HRT on the number of breast cancer diagnoses and deaths, separately. We found that mammography in the screening programme and outside the programme and the use of HRT could not explain the increase in the number of diagnoses. Probably other factors have caused more breast cancers in the past years. We estimated that 1-13% of all diagnoses were overdiagnosed. This means that women who get a diagnosis of breast cancer in the screening age have a chance varying between 1% and 13% of having an overdiagnosed cancer. The cost-effectiveness of the NBCSP ranges from NOK 131,078- NOK 396,572 per quality adjusted life year (QALY) gained, which is cost-effective (threshold between NOK644,680 and NOK 1,926,366).

We will address 1 of the 3 suggested main evaluation topics: evaluation of the cost-effectiveness of breast cancer screening in Norway. Using the micro-simulation analysis model MISCAN, the short- and long-term effects, risks and costs of mammography scre ening in Norway will be assessed. First, MISCAN will be calibrated using Norway-specific demographic and epidemiologic characteristics, the clinical breast cancer incidence before and after the implementation of screening, and the characteristics of the N orwegian screening program (attendance rates, screening interval, detection- and interval cancer rates). The observed breast cancer mortality in Norway is then compared to the model predictions. Because MISCAN incorporates the results of the randomized co ntrolled breast cancer screening trials, a difference between observed and predicted outcomes is an indicator of the effectiveness of the Norwegian screening program compared to international findings. With the calibrated model, the breast cancer mortalit y reduction, (quality adjusted) life years gained, number needed to screen, prevention of advanced disease and the number of over-diagnosed breast cancers is predicted. We assume that the current program, biennially inviting women aged 50-69, would be con tinued until 2025. The short- and long term direct and indirect costs of mammography screening in Norway, including the costs of over-diagnosis, over-treatment and false-positive test outcomes, are then predicted. To account for all potential screening ef fects, effects and costs are calculated over the whole period that the simulated population is alive. Cost-effectiveness is calculated as the difference in total costs between a situation with screening and a situation without screening, divided by the di fference in life-years between a situation with screening and a situation without screening. A sensitivity analysis is performed for the main model parameters.

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MAMMOGRAFI-Evaluering av Mammografiprogr

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