MRI has a high false positive rate for women with a hereditary risk of breast cancer
Magnetic resonance imaging (MRI) falsely detects breast cancer in five out of every six positive scans according to new research into the use of MRI for women with a high, inherited risk of developing the disease.
The study, published today in Annals of Oncology also showed that MRI was very good at detecting genuine cases of invasive cancers and ductal carcinoma in situ (DCIS), although the authors said that improvements in detection were still necessary.
The researchers from the Hereditary Cancer Clinic at Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands, followed 196 women with a BRCA1 or BRCA2 mutation, aged between 21 and 68 for an average of two years. Once the women had discovered that they carried a BRCA mutation they made six-monthly visits to hospital to be examined by an experienced medical specialist and to have a mammography and, whenever possible, MRI. During the period of the study, which ran from 1999 to 2005, 41 per cent of the women had at least one positive MRI or mammogram; breast cancer was detected in 17 women (11 from scanning, four during prophylactic mastectomy and two during the interval between surveillance visits). The researchers found that the sensitivity of mammography was 41 per cent, for MRI it was 60 per cent and for the two combined it was 71 per cent. The specificity of the techniques was 93 per cent for mammography and 90 per cent for MRI or a combination of the two.
The lead author of the study, Dr Nicoline Hoogerbrugge, said: “When we looked at the positive MRI results, we found that 83 per cent of them could not be confirmed histologically and were, therefore, false positives: five out of every six positive MRI scans.”
The researchers also found that approximately six per cent of the BRCA mutation carriers who had normal findings from their clinical surveillance, mammograms and MRIs, and who underwent an intended prophylactic mastectomy, had an unsuspected malignancy. One was only four millimetres in size and it is known that MRI and mammograms have difficulty detecting lesions this small, but three were DCIS between six and 15mm. “This indicates that further improvement of early breast cancer detection is still necessary,” said Dr Hoogerbrugge. During their first surveillance visit, the researchers recorded whether the women had a preference for ongoing surveillance, or prophylactic mastectomy and/or a prophylactic salpingo-oophorectomy (removal of fallopian tubes and ovaries). 30 per cent (58 women) expressed a preference for a prophylactic mastectomy. Three had no preference, and the rest preferred to have ongoing surveillance. After some of these women had a positive scan, mastectomy was carried out in 90 per cent of those women who had expressed a preference for it, and in only 31 per cent of those who had preferred surveillance.
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