EVALUATION OF THE NET BENEFIT OF BREAST CANCER MASS-SCREENING: AN ANALYSIS OF BENEFIT AND HARM USING A MATHEMATICAL MODEL OF AGE SPECIFIC POPULATION DYNAMICS

Purpose: In contrast to the downgraded recommendation by the U.S. Preventive Services Task Force (USPSTF) for breast cancer screening for women aged 40–49 years in 2009, Japanese women in their 40s have been successively encouraged to attend breast cancer screenings since 2004. The aim of this study is to examine whether these different mass-screening strategy is justifiable by the different situations of these countries and to find out the best strategy.

 Methods: We used a mathematical model of age specific population dynamics. The model is also specific to the stages of breast cancer progression and screening status (i.e., cancer has been detected or not yet). The basic demographic parameters of the model were obtained from health statistics and transition probabilities were estimated to be fit to observed data in Japan and US. Performance of screening strategies (biennial intervals; initiating/terminating ages) was evaluated. Benefits (extended average life expectancy) and harm (false-positive results) of these strategies were calculated. To evaluate net benefit of each strategy, critical increase of average life expectancy was calculated. If the harmful effect produced by false positive can be larger than the critical value, then it implies that the net benefit of mass-screening should be invalidated. The benefit of mass-screening depends on the degree of mortality reduction due to medical care provided after the detection of cancer. Sensitivity analysis was performed as to this aspect because of the lack of data.

 Results: Critical increases of average life expectancy in age group 40–69 and 50–69 years in Japan were 58 and 69 days. They were 109 and 138 days in US. According to the result of sensitive analysis on the degree of reduced mortality due to medical care, the robustness of this conclusion was retained. The best strategy was dependent on the actual harm level of the false positive in Japan and US.  

Conclusions: The critical increase of average life expectancy was calculated to be ca. 55 days in Japan and ca. 120 days in US. If the harmful effect produced by false positive can be estimated below the critical increase in each country, mass-screening of breast cancer should have net advantage taking harmful effect into account. The conclusion was retained independent of the levels of mortality reduction due to early starting medical care.