Cancer overdiagnosis in mammography screening programmes

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Screening for cancer may detect cancers that will not cause symptoms or death (overdiagnosed cancers). In autopsy studies of women aged 40–54 who died of causes other than breast cancer, 37% had invasive or non-invasive cancer. A systematic review has shown a high rate of overdiagnosis in mammographic screening programmes.

Data were analysed from publicly organized mammography screening pro­grammes in the United Kingdom, Canada, Australia, Sweden and Norway. Overdiag­nosis of breast cancer was estimated at 52%. There was an increase in incidence of breast cancer after the introduction of screening, but only a small drop in incidence in previously screened women.

It is concluded that one in three breast cancers detected in a population offered organized screening is overdiagnosed.

Jørgensen KJ, Gøtzsche PC. Overdiagnosis in publicly organised mammography screening programmes: systemic review of incidence trends. BMJ 2009;339:206–209; Welch HG. Overdiagnosis and mammography screening. Ibid:182–183 (comment).