Background: Overdetected breast cancers (BCs) via mammography screening that are biologically nonprogressive and unnecessary to receive treatment is of great concern for population-based screening. Most previous studies estimated overdiagnosis by excess incidence due to the introduction of screening compared with background incidence derived from randomized control trial, which require population incident-based BC data and the strong assumption of lead-time distribution, few studies have been adopted by using merely follow-up data on BCs. Aim: To assess respective independent contributions of overdiagnosis and curation to long-term breast cancer survival by the application of the novel zero-inflated statistical model to a longitudinal follow up empirical data with sufficient information based on patient-based data. Methods: We designed a retrospective cohort composed of 1346 patients diagnosed with invasive breast cancer in Falun Central Hospital of Dalarna County, Sweden, through international collaboration. A novel zero-inflated cured or overdiagnosis regression model was conducted. The zero part represents both types of nonprogressive cancer without potential of dying from BC, the cured due to treatment and the overdiagnosed due to mammography screening. These 2 types would be distinguished by detection modes (screen-detected cases and interval cancer plus cancers from nonparticipants). The count part represents the progressive breast cancer with potential of dying from BC associated with prognostic factors during follow-up. Results: The probability for nonprogressive BC (the zero part) was 56.14%. The probability of zero due to curation resulting from early detection and effective treatment was 44.34%. Overdiagnosis resulting from mammography screening program was 8.94% and high awareness was 2.86%. Among 43.86% progressive BC (the count part), 32.11% patients undergoing subsequent adjuvant therapies still remained alive after 15-year follow-up when adjusting for significant prognostic factors. The 15-year prognosis-adjusted cumulative survival of BC was dropped from 88.25% to 74.80% after correcting for the zero-inflated part of overdiagnosis. Conclusion: The proposed zero-inflated model with 15 years of follow-up data revealed 12% due to overdiagnosis after taking out the probability of zero due to curation as a result of early detection and effective treatment from the total zero part.
Social differences in breast cancer survival in relation to patient management within a National Health Care System (Sweden)