Breast MRI with USPIO contrast helps assess lymph node metastases

By Cynthia E. Keen, AuntMinnieEurope.com staff writer

April 25, 2008 -- Austrian researchers have found that breast MRI with a contrast medium based on ultrasmall superparamagnetic iron oxide (USPIO) particles could help avoid mastectomy for women whose breast cancer has not spread to the lymph nodes. But further development of the technique could be limited by the investigational nature of the contrast agent.

USPIO-enhanced MRI imaging shows promise as a valuable tool for both surgical planning of breast carcinoma and determining if preoperative adjuvant therapy is needed, according to Dr. Mazda Memarsadeghi from the Medical University of Vienna. Memarsadeghi presented research on the technique at the 2008 European Congress of Radiology (ECR) in Vienna.

If a USPIO-enhanced MRI scan finds metastatic nodes in a patient who is scheduled for sentinel node lymphadenectomy, conventional surgical lymph node dissection may be more appropriate. If no malignant nodes are identified, breast conservation surgery with sentinel node dissection may be recommended in lieu of a mastectomy and/or lymph node dissection.

Breast cancer patients would benefit from a noninvasive imaging technique that allows accurate preoperative assessment of axillary nodes. Between 40% and 70% of these patients have histopathologically negative axillary lymph nodes, and surgical complications from lymph node dissection include numbness, recurring underarm pain and discomfort, limitations of shoulder movement, seroma formation, and lymphedema.

Imaging techniques for differentiating nonmetastatic and metastatic lymph nodes vary widely. The Austrian researchers chose to examine the use of Sinerem, a work-in-progress USPIO-based contrast agent developed by Guerbet of Roissy, France.

The agent is a nanoparticle composed of an iron oxide core coated with low molecular weight dextran, and allows the identification of malignant nodal infiltration independent of lymph node size. The researchers used Sinerem on an investigational basis, as the product has not yet received marketing authorization in Europe.

Normal lymph nodes are distinguished from metastatic ones based on signal intensity characteristics. After intravenous USPIO administration, nonmetastatic lymph nodes generally show uptake of contrast material, which results in decreased signal intensity on T2- and T2*- weighted MR images.

The Austrian group used Sinerem to identify metastases in lymph nodes of 22 patients diagnosed with breast cancer. Patients were scanned on a 1-tesla MRI system (Gyroscan T10-NT, Philips Healthcare, Andover, MA).

The cohort included 22 consecutive women age 40-79 (mean age 60), whose images were evaluated on axial T1-, axial T2-, and axial T2*-weighted sequences. Inclusion criteria included the following:

Patients with breast carcinoma confirmed histopathologically by using percutaneous image-guided core breast biopsy at presentation
Patients with at least one lymph node that could be potentially compared with one lymph node available for histopathologic analysis at presentation
Patients scheduled to undergo surgery within 15 days.

Visual analysis of the USPIO-enhanced images was performed using a PACS diagnostic workstation. After evaluation, prints were produced and lymph nodes were marked.

From a total of 279 lymph nodes, a node-by-node evaluation could be achieved for 133. Of these, 13 (10%) were metastatic and 120 (90%) were nonmetastatic. For the evaluated nodes, the technique yielded impressive results on a node-by node analysis by researchers: 100% sensitivity, 100% specificity, and 100% accuracy.

The researchers also compared the results of this study with another study they published in 2006 in Radiology that compared the accuracy of nonenhanced versus USPIO-enhanced MR (Radiology, November 2006, Vol. 241:2, pp. 367-377).

Because the researchers wanted to see if they could avoid performing the nonenhanced study prior to the contrast exam, they decided to replicate the study two years later to validate their original analysis, Memarsadeghi explained.

The same two radiologists who read the images in the 2006 study also read them in the current research, but were blinded to prior results. In the original study, nonenhanced images on a node-by-node evaluation had a 55% sensitivity, 81% specificity and accuracy of 79%. By comparison, USPIO-enhanced images on a node-by-node evaluation had a sensitivity of 100%, a specificity of 98%, and an accuracy of 98%.

Although the results are positive, the university does not routinely use Sinerem because of the product's investigational status. Memarsadeghi recommended that additional studies be done to confirm their results.

"A larger prospective study should be performed to validate our observations by ascertaining the accuracy of the technique in the detection of nodal metastases," he said. "Further studies with different imaging analysis protocols are needed, as well as a comparative study necessary to demonstrate the potential benefit of USPIO-enhanced MR imaging as a diagnostic tool."

By Cynthia Keen
AuntMinnie.com contributing writer
April 25, 2008