Breast Cancer - Screening

Breast MRI

Magnetic resonance imaging (MRI) has been shown to detect cancers not visible on mammograms, but has long been regarded to have disadvantages. For example, although it is 27-36% more sensitive, it is less specific than mammography. As a result, MRI studies will have more false positives (up to 5%), which may have undesirable financial and psychological costs. It is also a relatively expensive procedure, and one which requires the intravenous injection of a chemical agent (from which there are side effects, potentially serious in a small number of people) to be effective. Proposed indications for using MRI for screening include:

• Strong family history of breast cancer
• Patients with BRCA-1 or BRCA-2 tumour suppressor gene mutations
• Evaluation of women with breast implants
• History of previous lumpectomy or breast biopsy surgeries
• Axillary metastasis with an unknown primary tumor
• Very dense or scarred breast tissue

However, two studies published in 2007 demonstrated the strengths of MRI-based screening:

• In March 2007, an article published in the New England Journal of Medicine demonstrated that in 3.1% of patients with breast cancer, whose contralateral breast was clinically and mammographically tumor-free, MRI could detect breast cancer. Sensitivity for detection of breast cancer in this study was 91%, specificity 88%.
• In August 2007, an article published in The Lancet compared MRI breast cancer screening to conventional mammographic screening in 7,319 women. MRI screening was highly more sensitive (97% in the MRI group vs. 56% in the mammography group) in recognizing early high-grade Ductal Carcinoma in situ (DCIS), the most important precursor of invasive carcinoma. Despite the high sensitivity, MRI screening had a positive predictive value of 52%, which is totally accepted for cancer screening tests. The author of a comment published in the same issue of The Lancet concludes that "MRI outperforms mammography in tumour detection and diagnosis."