The Evolving Role of Magnetic Resonance Imaging in the Screening for and Evaluation of Breast Cancer
Breast cancer remains the commonest cancer and the top cancer killer among women in Singapore. Approximately 1 in 17 women in Singapore will develop breast cancer during their lifetime. As there is insufficient understanding of its cause, prevention is not possible. Thus, the feasible strategy for reducing deaths lies in early detection, careful diagnostic evaluation, and effective therapy.
The introduction and widespread use of mammography for early detection of breast cancer is one of the most important achievements in the control of the disease. In Singapore, a nation-wide mammography-based screening programme, BreastScreen Singapore, was launched in 2002. Annual screening is recommended for women aged 40-49 years and twice yearly for those 50 and above.
Breast MRI is not recommended as a routine screening tool for breast cancer. However, for women at high risk, annual breast MRI is recommended. Contrast-enhanced MRI uses magnets and radio waves to create 3-dimensional images of the breast tissue. The woman lies prone (on her stomach), on a padded platform with windows for the breasts. The platform slides into a tunnel-like machine, which makes a loud thumping noise. The examination takes 30 to 45 minutes. A contrast solution (dye) is injected into a vein in the arm at the start of the test. The contrast tends to be concentrated in areas of cancerous growth, which shows up as white areas against black or grey normal breast tissue.
1. Contrast-enhanced breast MRI.
A cancerous lump appears white on MRI (circled) while normal breast tissue appears black or grey.
MRI is more sensitive in finding cancers, especially in dense
breasts, and finding very small lesions when compared to mammography and
breast ultrasound. However, the test does have disadvantages. It is associated
with more false positives, i.e., the test shows something, which looks suspicious
but turns out to be non-cancerous upon biopsy. MRI is a lot more expensive
than a mammogram or ultrasound, costing 6 to 8 times more.
High risk women are those with a strong family history of breast and/or ovarian cancer, or carriers of mutations in BRCA1 or BRCA2 genes (breast cancer susceptibility genes), or women who have received radiation therapy to the chest in the first three decades of life. Women who have relatives with breast and/or ovarian cancer should have their degree of risk assessed at a cancer genetics or risk assessment/prevention clinic. Many women with a family history do not fall into the high-risk category. Women at high risk tend to develop breast cancer at a younger age and have tumour sub-types that could be missed on mammography. Thus, annual contrast-enhanced breast MRI, in addition to mammography is recommended for this group.
MRI is also useful in certain women with newly diagnosed breast cancer. In women considering breast-conserving surgery (lumpectomy or wide local excision), a breast MRI before surgery should be considered if the tumour if difficult to see and measure using mammography and ultrasound. MRI gives a more accurate assessment of the extent of the disease, especially for women with dense breasts or a particular type of cancer called invasive lobular carcinoma. The finding of a larger tumour would allow the surgeon to plan for a wider area of excision if conservation is still possible. Otherwise, mastectomy should be undertaken.
Breast MRI may detect more areas of cancerous change when only one area was detected on mammography and ultrasound. In such a situation, mastectomy would be more appropriate. Some women who present with larger tumours may be given chemotherapy before surgery. Evaluation of the breast cancer with MRI before and after chemotherapy is useful to define the extent of disease, the response to treatment and the potential for breast conserving surgery after chemotherapy.
Figure 2. Breast MRI of a patient who received chemotherapy before breast surgery.
(A) At diagnosis, MRI showed a large tumour in the breast (circled).
(B) Repeat MRI after a course of chemotherapy showed very good response to chemotherapy, with hardly any visible tumour. The patient subsequently underwent a lumpectomy.
MRI is increasingly available in many centres, but breast MRI should be interpreted by dedicated breast radiologists and performed in centres where MRI guided breast biopsy is available. Otherwise, a biopsy cannot be done to establish the diagnosis of suspicious lesions detected only on MRI but are not visible on mammogram and ultrasound.
In Singapore, up to a year ago, when biopsy of breast lesions detected only on MRI was necessary, the only option was surgical/excision biopsy with MRI-guided wire localisation. This involves the use of MRI to guide the insertion of a wire into the breast to mark the location of the lesion before surgery, followed by surgery under general anaesthesia to remove the lesion.
Now, MRI-guided needle biopsy is possible. MRI-guided vacuum-assisted core needle biopsy is a minimally invasive procedure performed under local anaesthesia and obviates the need for surgery. The availability of this service is very limited. The National Cancer Centre Singapore is the first and only centre in the Asia-Pacific to perform this procedure, using the Mammotome MR Biopsy System.
This is performed in the MRI Suite by dedicated breast radiologists and surgeons. The woman lies prone on the platform in the MRI machine for approximately 45 to 60 minutes. The procedure involves the single insertion of a needle equipped with a vacuum device into the breast through a 0.5cm incision under MRI guidance. The device cuts, vacuums and partially or completely removes the breast lesion for microscopic examination. At the end of the procedure, only an adhesive bandage is used to cover the incision. Most patients are able to return to normal activity the next day.
Figure 3. MRI-guided vacuum-assisted core needle biopsy of a breast lump.
(A) A MRI scan is performed to identify the location of the lump to be biopsied (circled). (B) The Mammotome MR Biopsy needle is inserted into the breast after local anaesthetic has been injected into the skin and breast tissue. A repeat MRI confirms the correct position of the needle before tissue is extracted.
MRI-guided needle biopsy has clear advantages over excision biopsy with MRI-guided wire localisation. As more women undergo breast MRI, either for screening or for thorough evaluation of a breast cancer, the role for MRI guided needle biopsy will become increasingly important.
Dr Ho Gay Hui, Senior Consultant, Dept of Surgical Oncology &
Dr Jill Wong, Senior Consultant, Dept of Oncologic Imaging, National Cancer Centre Singapore.
Other write-ups that may be of your interest
- Staying Positive Was Her Strategy
- Symptoms of Breast Cancer
- The Evolving Role of Magnetic Resonance Imaging
- Breast Self Examination (BSE)
- What is a Mammogram? Is it for me?
- Myths and Truths About Breast Cancer