Microbubble contrast-enhanced ultrasound was used to identify nearly 90 percent of sentinel lymph nodes prior to breast cancer surgery, opening up the possibility to employ pre-operative ultrasound to spare patients an additional tumor-staging surgery, according to a study published in the February issue of the American Journal of Roentgenology.
“Axillary nodal status remains the most important prognostic factor in patients with breast cancer and determines adjuvant treatment,” emphasized Ali R. Sever, MD, of the department of radiology at Maidstone Hospital in Maidstone, England, and colleagues.
Sentinel lymph node (SLN) biopsy, performed during tumor resection, is the standard procedure for axillary staging. If SLNs come back positive for metastases, though, a separate axillary lymph node (ALN) dissection surgery becomes necessary for ALN staging, which is associated with additional complications and costs.
“The aim of this study was to identify and localize SLNs preoperatively by contrast-enhanced sonography after intradermal injection of microbubbles in patients with breast cancer,” Sever and co-authors reported. Previous trials have taken place only in animals, while the potential for such imaging could allow patients with preoperatively identified metastases to bypass SLN biopsy and undergo ALN dissection during resection surgery, thereby saving SLN-positive patients from a second ALN-dissection surgery.
Seventy-eight women and two men with primary breast cancer received a periareolar intradermal injection of microbubble contrast agent. A gray-scale ultrasound exam of the axilla was performed prior to the injections, with pulse-sequenced imaging of the lymphatic channels conducted post-injection. Areas of contrast agent accumulation were then imaged with gray-scale or live dual images to confirm the presence of the architecturally defined lymph nodes. If necessary, massage or up to two additional injections were given, after which no nodal visualization was considered a failure.
SLNs were identified in 71 of 80 patients, with guidewire successfully inserted in all cases. Gray-scale images revealed clearly visible lymph nodes in 43 patients, while in 25 patients SLNs were identifiable only after microbubble enhancement. In three cases, guidewire was inserted into areas of pooled contrast agent, without a recognizable SLN architecture available on images.
Of the nine failed procedures, one was caused by a technical ultrasound machine error and three by non-visualized breast lymphatics. Three SLNs were visible but non-draining, while in two cases nodes were visible only by gray-scale. During surgery, it was discovered that these last two nodes were not, in fact, SLNs, but ALNs. “This emphasizes the importance of contrast enhancement in assisting successful SLN identification,” the authors argued.
Fourteen patients were found to have metastases in SLNs, all of which were identified under ultrasound and localized with guidewire prior to surgery. Of the nine patients in whom ultrasound did not identify the draining SLNs, six had invasive ductal carcinomas smaller than 20 mm, two had grade II invasive lobular carcinomas, also smaller than 20 mm, and one had a 34 mm grade II invasive lobular carcinoma.
Highlighting the advantages introduced by the authors’ findings, an accompanying commentary noted that: “The true clinical challenge is to evaluate whether the use of ultrasound contrast materials has a role in delineating intranodal morphology (perfusion defects) that may help differentiate benign from malignant disease in vivo,” wrote Wei Tse Yang, MBBS, professor of diagnostic radiology at the University of Texas MD Anderson Cancer Center in Houston, and Barry B. Goldberg, MD, of the Jefferson Ultrasound Research and Education Institute at Thomas Jefferson University Hospital in Philadelphia.
Yang and Goldberg also reiterated the importance, expressed by the authors, of continued research trials to determine the most effective agents for imaging SLNs. Sever and colleagues noted that the success rate of the preoperative procedure will likely improve with increased trials.
Still, Yang and Goldberg stressed the potential benefits to patient outcomes of this first in vivo trial, saying: “Patients with biopsy-proven metastases will therefore not require surgical SLN biopsy and can proceed directly to axillary nodal dissection.”