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Mammography screening:
adverse effects warning

Breast cancer screening by mammography can lead to serious adverse effects.

Like any medical intervention, mammography screening carries the risk of adverse effects, in particular "false positives" and overdiagnosis.

Mammograms can produce "false positive" results (i.e. the detection of an anomaly which subsequently turns out not to be malignant). In 2003, mammogram results showing an abnormal result caused some 70,000 women in France unnecessary anxiety. These false positives lead to pointless further tests, some of which are aggressive, such as surgical biopsies of the breast. These tests themselves can cause physical and psychological adverse effects.

Furthermore, although screening does detect a certain number of breast cancers, they are often cancers which would never have caused the woman to suffer or caused her death: it is a question of overdiagnosis. According to some studies, around 30% of invasive breast cancers and a high proportion of microscopic cancers (ductal carcinoma in situ) detected by mammography are examples of such overdiagnosis. The treatment of cancers detected by over-zealous diagnosis does not offer any benefits to the women concerned, and causes adverse effects: removal of all or part of the breast, adverse effects from chemotherapy etc.

All these adverse effects of mammography screening weigh in the benefit-harm balance of this form of screening, which participants should be entitled to know about.

©Prescrire May 2006

Source: "Les effets indésirables des mammographies de dépistage des cancers du sein " Rev Prescrire 2006 ; 26 (271) : 269-275.

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