Finding cancer at an early stage does not always reduce a woman’s risk of dying from breast cancer. Even though mammography can detect malignant tumours that cannot be felt, treating a small tumour does not always mean that the woman will not die from the cancer. A fast-growing or aggressive cancer may have already spread to other parts of the body before it is detected. Screening might not help prolong the life of women with such tumours, but women with such tumours would live a longer period of time knowing that they may have a fatal disease. In addition, screening mammograms might not help prolong the life of a woman who is suffering from other, more serious health conditions.

X-rays have the potential to cause cancer. Mammograms require small doses of radiation, so the risk of harm from this radiation exposure is low. The benefits of mammography screening in organized programmes outweigh the potential harm from the radiation exposure.

False-positive results occur when radiologists find a mammographic abnormality although no cancer is actually present. All abnormal mammograms should be followed up with additional testing (diagnostic mammography, ultrasound, and/or biopsy) to determine whether cancer is present. False-positive mammogram results may lead to anxiety and other forms of psychological distress that usually are not long-lasting. The additional testing required to rule out cancer can also be time-consuming and can cause physical discomfort. European quality standards are designed to minimize waiting times and reduce the associated anxiety.

Over a 20-year period, about 1 out of 5 women regularly participating in screening will receive a false-positive result that can be clarified without invasive procedures. Over the same period, about 1 out of 10 women will require an invasive procedure (using a needle to take small samples of breast tissue) without an operation, and up to about 1 out of 100 women will undergo an operation to check the result of the mammography.

Another risk is that a breast cancer could be found at screening that neither you nor your doctor would ever have found if you had never gone to screening – this is called overdiagnosis. Unfortunately, it is not possible to distinguish which of the cancers detected at screening are overdiagnosed. On average 5-10 out of 100 cancers detected at screening are estimated to be overdiagnosed. The risk is lower for young women and higher for older women.