Early breast cancer: MRI v mammography

High-tech magnetic resonance imaging (MRI) scans are more effective at detecting early cases of breast cancer than x-ray based mammograms, reported_ The Guardian_ . It explained that  “X-ray based mammograms detect only 56% of early lesions in high-risk women compared with 92% when MRI scans” are used. 

Most cases of breast cancer begin with non-invasive cancerous cells in the milk ducts – called ductal carcinoma in situ (DCIS) – which “if detected and quickly treated prevent the disease’s progression” the newspaper said. It quoted the researchers as saying that “if you picked up all cases of ductal carcinoma in situ you would prevent virtually all cases of breast cancer”.

The Guardian says that this study’s finding “raises new questions about the national breast cancer screening programme”.

This study provides reliable evidence that using MRI is better at detecting this early breast cancer than mammography in a particular group of women (the study was not conducted using a sample of women that reflects the general population). This research does not support the introduction of MRI into a national breast cancer screening programme at present. However, it is an interesting finding and further research should be conducted to assess the effects of MRI screening in the general population. 

Where did the story come from?

The research was conducted by Christiane Kuhl and colleagues at University of Bonn, Germany and was published in the journal, The Lancet .

What kind of scientific study was this?

This was a diagnostic study investigating the ability of MRI and mammography to detect a particular form of early breast cancer – ductal carcinoma in situ (DCIS).

The researchers recruited 7,319 women who then underwent a mammography and a breast MRI at the University of Bonn Hospital and Medical School, and these were interpreted independently by different radiologists. If one of the imaging tests was positive or there were clinical signs of breast cancer, the patient had a biopsy to assess for DCIS.

What were the results of the study?

Among the women who were found to have this particular form of early breast cancer after biopsy, MRI detected 92% of cases compared with 56% of cases detected by mammography. MRI was particularly effective relative to mammography in women with high-grade ductal carcinoma in situ (DCIS). Among women with a positive MRI screening test, DCIS was confirmed using a biopsy in 59% of cases with MRI and 55% of cases with mammography.

What interpretations did the researchers draw from these results?

The researchers concluded that using MRI screening may improve the ability to diagnose this form of early breast cancer – ductal carcinoma in situ (DCIS), particularly high grade DCIS.

What does the NHS Knowledge Service make of this study?

This is a well-conducted study, which provides reliable evidence that MRI detects a greater proportion of women with ductal carcinoma in situ (DCIS) than mammography. There are some limitations to the interpretation of results from this study, which are acknowledged by the authors:

• The group of women that participated in the study are not representative of the general population who currently receive regular mammography screening. Therefore, it is not appropriate to make recommendations regarding the use of MRI for general population breast cancer screening.  
• The radiologists reading the MRI scans were blinded to the results of mammography scans. However, they are likely to be aware of the fact that most women referred for MRI and included in the study are likely to be at high risk of breast cancer or have a positive mammography result; this potentially increases suspicion when interpreting the MRI results and leads to bias. 
• There is some uncertainty regarding the prognosis of women found to have DCIS, as it may not always lead to life-threatening breast cancer. Despite this uncertainty, there is consensus that the diagnosis of high-grade DCIS, before progression to invasive breast cancer, is important in terms of eventual outcome.
• From this study, no interpretations can be made on the use of MRI or mammography for detecting the other, less common, pre-cancerous form of lobular carcinoma in situ (LCIS – cancer of the milk glands rather than the ducts).