Screening technologies used to diagnose breast cancer are unable to distinguish between harmless and malignant tumours, a study has found.
The report by the Nordic Cochrane Centre in Denmark claims that one in three breast cancer cases diagnosed by mammograms are harmless and can lead to women undergoing invasive treatment needlessly.
The study, which looked at data from the UK, Canada, Australia, Sweden and Norway, suggests that ‘overdiagnosis’ of cancer can affect up to 59 per cent of those undergoing treatment.
Writing in the British Medical Journal (BMJ), the researchers said: ‘Screening for cancer may lead to earlier detection of lethal cancers but also detects harmless ones that will not cause death or symptoms.
‘As it is not possible to distinguish between lethal and harmless cancers, all detected cancers are treated. Overdiagnosis and over-treatment are therefore inevitable.’
The results re-open the discussion surrounding existing screening technology, which uses low-dose X-rays that pass through the breast to an image receptor.
The NHS Cancer Screening Service predicts the technology saves 1,400 lives every year. However, the researchers of the report pointed to post-mortem data suggesting that for each woman saved, up to 10 will be overdiagnosed.
A spokesperson for the NHS said that it is in the process of replacing its film-based mammographs with digital imagery. While this would reduce the number of false positives, it would be insufficient to combat overdiagnosis.
Dr David Smith, a researcher at Northumbria University, believes that the solution lies in the development of technology such as microwave screening to provide earlier detection and eliminate the need for surgery.
Smith said: ‘Some tumours that turn out to be malignant have different material properties to tumours that are not threatening. We are working on determining this difference as well as using microwaves for early-stage detection. However, research is still at an early stage and there are some significant technical challenges to this.’
These technical challenges lie in the fact that unlike X-rays, microwaves do not travel in straight lines meaning that reconstruction of the image is currently based on mathematical approximation. However, Smith is confident that once this is resolved the use of microwaves can provide a more effective method of detection.
He added: ‘Our ultimate aim is to eventually have a low-cost and inherently safe screen technique that could replace X-ray mammography and we believe microwave technology can do this. Initial studies have shown that it is able to provide sufficient resolution and can pick up tumours in the order of 3-5mm, which will reduce the need for intensive treatment.’
Pamela Goldberg, chief executive of Breast Cancer Campaign, believes that until research progresses, X-ray screening should play a crucial role in breast cancer diagnosis and treatment.
She said: ‘Screening is an important tool in the early detection of breast cancer. Until research can identify which pre-invasive cancers, such as ductal carcinoma in situ (DCIS), will develop into invasive and potentially life-threatening breast cancer, the NHS breast-screening programme plays a valuable role.’Ellie Zolfagharifard