Abstract
Abstract OBJECTIVES: The aim of the current study was to estimate age-specific overdiagnosis due to mammography screening in the two randomized trials in Malmö, Sweden: The Malmö Mammographic Screening Trial I and II (MMST I and MMST II). SETTING: Women living in Malmö were randomized in a 1:1 proportion to a screening group or a control group. The MMST I included 42,283 women born between 1908 and 1932 and the MMST II included 17,793 women born between 1933 and 1945. Women in the study group were invited from 1976 until 1990 when the control group was invited. The age at randomization was 45-70 years in MMST I and 43-48 years in MMST II. METHODS: Data from the two trials were merged and overdiagnosis was estimated using age specific incidence rates excluding the first years of screening. The age specific relative breast cancer incidence rate for the screening group versus the control group was estimated and adjusted for lead time. Only the first breast cancer diagnosis was considered and results for invasive cancer and carcinoma in situ combined as well as for invasive cancer were calculated. RESULTS: The number of breast cancer cases, including carcinoma in situ, for the period 1976-1989 was 867 and 676 for the study group and the control group, respectively. The rate ratio for overdiagnosis in age 43-78 years adjusted for lead time was 1.04 (95% CI, 0.93-1.16). No overdiagnosis from subsequent screening was found for women below the age of 60. In women aged 60-69 and 70-78 years overdiagnosis was estimated at 1.13 (0.95-1.33) and 1.15 (0.85-1.54), respectively. The corresponding results for invasive cancer only was lower and no overdiagnosis was seen except for the age group 60-69 years where the rate ratio was 1.10 (0.92-1.32). For age 43-78 the result was 0.96 (0.85-1.08). CONCLUSIONS For the total material overdiagnosis from subsequent screening, including carcinoma in situ, was 4%. This is somewhat lower than an earlier evaluation of MMST I where age were higher and another method was used. For women below the age of 60 no overdiagnosis was seen and indicated that the possible problem with overdiagnosis concern women 60+. However none of the results were statistically significant at the 5% level. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-04-02.
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