Overdiagnosis and overtreatment of breast cancer: Estimates of overdiagnosis from two trials of mammographic screening for breast cancer

Randomised controlled trials have shown that the policy of mammographic screening confers a substantial and significant reduction in breast cancer mortality. This has often been accompanied, however, by an increase in breast cancer incidence, particularly during the early years of a screening programme, which has led to concerns about overdiagnosis, that is to say, the diagnosis of disease that, if left undetected and therefore untreated, would not become symptomatic. We used incidence data from two randomised controlled trials of mammographic screening, the Swedish Two-county Trial and the Gothenburg Trial, to establish the timing and magnitude of any excess incidence of invasive disease and ductal carcinoma in situ (DCIS) in the study groups, to ascertain whether the excess incidence of DCIS reported early in a screening trial is balanced by a later deficit in invasive disease and provide explicit estimates of the rate of 'real' and non-progressive 'overdiagnosed' tumours from the study groups of the trials. We used a multistate model for overdiagnosis and used Markov Chain Monte Carlo methods to estimate the parameters. After taking into account the effect of lead time, we estimated that less than 5% of cases diagnosed at prevalence screen and less than 1% of cases diagnosed at incidence screens are being overdiagnosed. Overall, we estimate overdiagnosis to be around 1% of all cases diagnosed in screened populations. These estimates are, however, subject to considerable uncertainty. Our results suggest that overdiagnosis in mammography screening is a minor phenomenon, but further studies with very large numbers are required for more precise estimation

Initiators and promoters for the occurrence of screen-detected breast cancer and the progression to clinically-detected interval breast cancer

This work was supported by the Ministry of Science and Technology, Taiwan (MOST 103-2118-M-002-005-MY3). This study was also supported by the American Cancer Society through a gift from the Longaberger Company's Horizon of Hope Campaign

NUMBER NEEDED TO SCREEN: LIVES SAVED OVER 20 YEARS OF FOLLOW-UP IN MAMMOGRAPHIC SCREENING

Objective: To estimate the number needed to screen with mammography to save one life, based on a. stated amount of screening activity and long-term follow-up for breast cancer death. Setting: A randomised controlled trial of mammographic screening for breast cancer, with 77,080 women invited to screening and 55,985 not invited. The invited group was offered screening for seven years. Follow-up continued for a total of just over 20 years. Methods: Number needed to screen for seven years to save one life over 20 years was calculated by, dividing the number screened (not the number invited) by the total number of lives saved. Similarly, we calculated the number of mammographic examinations required to save one life. Results: We estimate that the number of women needed to screen for seven years to save one life over 20 years is 465 (95% Cl 324-819). The number of mammographic examinations needed to save one life was 1499 (95% Cl 1046-2642). Conclusions: The number needed to screen to save one life is smaller than has been reported in the past. Mammographic screening is effective in absolute terms as well as relative. Long-term follow-up. allowed us to estimate the absolute benefit with greater accuracy

NUMBER NEEDED TO SCREEN: LIVES SAVED OVER 20 YEARS OF FOLLOW-UP IN MAMMOGRAPHIC SCREENING

Objective: To estimate the number needed to screen with mammography to save one life, based on a. stated amount of screening activity and long-term follow-up for breast cancer death. Setting: A randomised controlled trial of mammographic screening for breast cancer, with 77,080 women invited to screening and 55,985 not invited. The invited group was offered screening for seven years. Follow-up continued for a total of just over 20 years. Methods: Number needed to screen for seven years to save one life over 20 years was calculated by, dividing the number screened (not the number invited) by the total number of lives saved. Similarly, we calculated the number of mammographic examinations required to save one life. Results: We estimate that the number of women needed to screen for seven years to save one life over 20 years is 465 (95% Cl 324-819). The number of mammographic examinations needed to save one life was 1499 (95% Cl 1046-2642). Conclusions: The number needed to screen to save one life is smaller than has been reported in the past. Mammographic screening is effective in absolute terms as well as relative. Long-term follow-up. allowed us to estimate the absolute benefit with greater accuracy

Screening opportunity bias in case-control studies of cancer screening

In case-control evaluations of cancer screening, subjects who have died from the cancer in question (cases) are compared with those who have not (controls) with respect to screening histories. This method is subject to a rather subtle bias, among others, whereby the cases have greater opportunity to have been screened than the controls. In this paper, we propose a method of correction for this bias. We demonstrate its use on two case-control studies of mammographic screening for breast cancer.cancer screening, case-control study, opportunity bias,