Evaluation of the overdiagnosis in breast screening programmes using a Monte Carlo simulation tool: a study of the influence of the parameters defining the programme configuration.

OBJECTIVES: To build up and test a Monte Carlo simulation procedure for the investigation of overdiagnosis in breast screening programmes (BSPs). DESIGN: A Monte Carlo tool previously developed has been adapted for obtaining the quantities of interest in order to determine the overdiagnosis: the annual and cumulative number of cancers detected by screening, plus interval cancers, for a population following the BSP, and detected clinically for the same population in the absence of screening. Overdiagnosis is obtained by comparing these results in a direct way. RESULTS: Overdiagnosis between 7% and 20%, depending on the specific configuration of the programme, have been found. These range of values is in agreement with some of the results available for actual BSPs. In the cases analysed, a reduction of 11% at most has been found in the number of invasive tumours detected by screening in comparison to those clinically detected in the control population. It has been possible to establish that overdiagnosis is almost entirely linked to ductal carcinoma in situ tumours. CONCLUSIONS: The use of Monte Carlo tools may facilitate the analysis of overdiagnosis in actual BSPs, permitting to address the role played by various quantities of relevance for them.

A Monte Carlo analysis of breast screening randomized trials.

PURPOSE: To analyze breast screening randomized trials with a Monte Carlo simulation tool. METHODS: A simulation tool previously developed to simulate breast screening programmes was adapted for that purpose. The history of women participating in the trials was simulated, including a model for survival after local treatment of invasive cancers. Distributions of time gained due to screening detection against symptomatic detection and the overall screening sensitivity were used as inputs. Several randomized controlled trials were simulated. Except for the age range of women involved, all simulations used the same population characteristics and this permitted to analyze their external validity. The relative risks obtained were compared to those quoted for the trials, whose internal validity was addressed by further investigating the reasons of the disagreements observed. RESULTS: The Monte Carlo simulations produce results that are in good agreement with most of the randomized trials analyzed, thus indicating their methodological quality and external validity. A reduction of the breast cancer mortality around 20% appears to be a reasonable value according to the results of the trials that are methodologically correct. Discrepancies observed with Canada I and II trials may be attributed to a low mammography quality and some methodological problems. Kopparberg trial appears to show a low methodological quality. CONCLUSION: Monte Carlo simulations are a powerful tool to investigate breast screening controlled randomized trials, helping to establish those whose results are reliable enough to be extrapolated to other populations and to design the trial strategies and, eventually, adapting them during their development.

A Monte Carlo tool to study the mortality reduction due to breast screening programs.

PURPOSE: To develop a Monte Carlo tool that permits to study the reduction in breast cancer mortality rate due to breast screening programs. METHODS: Simulations implement woman histories undergoing a screening program, include a model of survival after local treatment of invasive cancers and use distributions of time gained due to screening detection against symptomatic detection and overall sensitivity of the screening obtained previously. Mortalities for the whole woman population and for those women with ages within the range considered in the program have been calculated. RESULTS: For the whole woman population, a reduction in breast cancer mortality up to 29% has been found for a configuration that includes women aged between 50 and 70 years, with a screening interval of two years and 100% acceptance rate. If an acceptance of 70% is considered, this percentage reduces to 20%. If, in the same conditions, the program starts at 40 years, the reduction of the mortality reaches 24% while if the screening interval is one year, this percentage raises to 28%. If mortalities are calculated for those women with ages within the range included in the program these reductions are greater and no significant differences are found between the programs with age ranges [50-70] and [40-70]. In the model, radio-induced cancers have no effect in survival. CONCLUSIONS: The results agree reasonably well with those of different trials. Mortality reductions of 12%-20% (between two and four deaths per year and 10(5) women) are obtained only for acceptances above 50%. This could be considered as a threshold for the acceptance, which appears to be a critical parameter.