MRI for detecting breast cancer

Breast cancer is a major killer world wide. In USA it is the most common non-skin cancer and the second leading cause of cancer-related deaths in women. Approximately 500,000 deaths worldwide are related directly or indirectly to breast cancer. Presently mammography is used extensively for breast screening and is effective in picking up breast cancer at an earlier stage, thus, decreasing the mortality rates from breast cancer. While mammography is highly effective in detecting breast cancer, it is not foolproof. With the advent of MRI, instead of using mammography, some patients are requesting MRI to screen for breast cancer. Is this wise?

While MRI has a high sensitivity in detecting breast abnormality, it has a low specificity. In other words, MRI can over diagnose and give you more reading of ‘cancer’ when the actual abnormal appearance on the scan is not due to cancer. In high-risk groups, such as women with breast cancer gene (BRCA) mutations, MRI is likely to be more sensitive than mammography, ultrasound and clinical breast examination in detecting breast cancer earlier. The reasons for this are that BRCA1-associated breast cancers are more likely to have round, pushing margins and rare calcifications and other benign mammographic appearances. Childhood cancer survivors are another group of high-risk individuals who might benefit from MRI because these individuals have dense breast tissue which makes mammographic assessment more difficult. It is a challenge for doctors to detect early breast cancer in breasts augmented with silicone because cancerous changes may be misinterpreted as silicone-induced mastopathy. MRI is good for differentiating between cancerous changes and silicone induced nodularity.

In patients with axillary lymphadenopathy (swollen lymph glands in the armpit) due to an occult breast cancer (non-palpable and non-mammographically visible), MRI can help to detect a suspicious breast lesion. Sixty percent of patients with ductal carcinoma in situ (DCIS) may develop invasive breast cancer over a period of 10 years. In a German study involving 7000 women who were subjected to mammography and MRI over a 5-year period, MRI detected significantly more cases (92%) of any grade of DCIS than mammography (56%). The study found that MRI is better in diagnosing DCIS, especially those with high-grade DCIS (Lancet 2007; 370: 485 – 492). However, it must be emphasized that the role of MRI in DCIS is not fully established.

At the recent 92^nd Clinical Congress of the American College of Surgeons, it was stated that breast MRI is an essential tool in screening high-risk groups, assessing the extent of disease and follow-up. MRI also has a role in cases of unknown primary tumour and in assessing the response to chemotherapy. The American Cancer Society recommends a screening MRI for women who have 20 – 25% or greater lifetime risk of breast cancer, including those with a strong family history of breast or ovarian cancer and those treated for Hodgkin’s disease (CA Cancer J Clin 2007; 57: 75 – 89).

Like all high tech medical tools, MRI of the breast is not applicable to everyone. It has limitations and requires clear guidelines as to when it should be used. When used judiciously, MRI is invaluable in guiding the doctors in managing a case of breast cancer. When used inappropriately, MRI can over-diagnose breast cancer in someone without breast cancer, giving rise to unnecessary anxiety and worse still causing someone to undergo an unnecessary and potentially disfiguring operation. 

(For those interested in reading a recent review article on the role of MRI in screening, diagnosis and management of breast cancer, please consult Expert Rev Anticancer Ther 2008; 8: 811 – 817)