Incidence of breast cancer in Norway and Sweden during introduction of nationwide screening: prospective cohort study

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Abstract
Objective To determine whether any increase in the incidence of breast cancer in women detected by mammography is compensated for by a drop in the incidence after age 69, years when women are no longer invited for screening. Design Population based cohort study of incidence of breast cancer during the introduction of nationwide screening programmes. Setting Norway and Sweden. Participants All women aged above 30 years (1.4 and 2.9 million, respectively, in 2000). Main outcome measures Changes in age specific incidence rates of invasive breast cancer associated with the introduction of the screening programmes. Results As a result of screenin creening is defined as the detection of low malignancy lesions that otherwise would not be detected in a patient's lifetime. It is often argued that overdiagnosis is not a problem for screening in breast cancer.1–3 For example, Boer et al predicted a 31% increase in incidence of breast cancer in the Dutch mass screening programme that would be nearly fully compensated for by a strong drop in the incidence after age 69 years conclusionWithout screening one third of all invasive breast cancers in the age group 50-69 years would not have been detected in the patients' lifetime. This level of overdiagnosis is larger than previously reported