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

摘要

Objective To determine whether any increase in the incidence of breast cancer in women detected bymammography is compensated for by a drop in theincidence after age 69, years when women are nolonger invited for screening.Design Population based cohort study of incidence ofbreast cancer during the introduction of nationwidescreening programmes.Setting Norway and Sweden.Participants All women aged above 30 years (1.4 and2.9 million, respectively, in 2000).Main outcome measures Changes in age specificincidence rates of invasive breast cancer associatedwith the introduction of the screening programmes.Results As a result of screening the recordedincidence of breast cancer in women aged 50-69 yearsincreased by 54% in Norway and 45% in Sweden.There was no corresponding decline in incidenceafter the age of 69 years.Conclusions Without screening one third of allinvasive breast cancers in the age group 50-69 yearswould not have been detected in the patients' lifetime.This level of overdiagnosis is larger than previouslyreported.