Ultrasound Elastography Developments Lead to Increased Sensitivity of Malignant Nodes

Developments in ultrasonography, including ultrasound elastography, offer increased sensitivity for assessment of malignant nodes. Further, microbubbles were shown to reduce the need for completion axillary lymph node dissection (ALND) by 50 percent. These findings were presented this week at the ECR 2011.

Ultrasound elastography used in conjunction with conventional ultrasound demonstrates axillary lymph nodes (ALNs) and differentiates benign from malignant nodes. The method also potentially increases sensitivity of identifying abnormal nodes for biopsy.

Dr. Kathryn Taylor, from Addenbrookes Hospital, Cambridge, UK, was the lead investigator on the study. Researchers looked at imaging modalities for preoperative assessment of axillary metastases in suspected breast cancer. Due to the relatively high false negative rate with conventional ultrasound plus needle biopsy, the researchers investigated the sensitivity of ultrasound elastography as an adjunct to conventional ultrasound.

Elastography is based on the principle that malignant tissue is stiffer than non-malignant tissue. A conventional ultrasound can be used with some additional software for the elastography. Taylor explained that some form of stress is applied to the tissue and any resulting tissue deformation is assessed, and an elastogram is displayed visually as a grey-scale (white is soft and dark is stiff tissue) or a color-scale (red is soft and blue is stiff).

“In terms of ALNs, the gold standard is conventional ultrasound +/- needle biopsy, which is performed as routine practice in women with routine breast cancer, but we know that this carries a false negative rate of up to 30 percent of nodes which show normal morphology but are metastatic,” according to Taylor.

In this study, 50 women with suspected solid breast lesions received routine conventional ultrasound of ipsilateral ALNs followed by quasi-static ultrasound elastography using software from the University of Cambridge. “The ultrasound elastography was retrospectively scored one to four (blinded for histology) and compared to histology as reference standard,” Taylor said.

Results showed that adding ultrasound elastography to conventional ultrasound reduces the false positive rate from 44 percent to 19 percent. Twenty-seven were morphologically normal on conventional ultrasound of which five were malignant at surgical histology. Importantly, all five were suspicious/malignant (score 3/ 4) on ultrasound elastography. Adding ultrasound elastography to conventional ultrasound raises sensitivity by 24 percent.

“Of the 21 ultimately positive in histology, 15 were correctly identified by ultrasound elastography as positive, and an additional four from the conventional ultrasound arm. Remember this scenario, unlike that of elastography of breast lesions where we are more interested in specificity than sensitivity because we want to avoid unnecessary biopsy, in the axilla, within reason, we are more interested in sensitivity to avoid unnecessary surgical sentinel lymph node biopsy,” according to Taylor

The results showed sensitivity of ultrasound elastography of 90 percent and specificity of 86 percent.

At the same session on ultrasound developments, Dr. Ali Riza Sever from Maidstone Hosptial, UK, presented results from a study which evaluated use of microbubbles to identify involvement of the sentinel ymph node (SLN) compared to SLN biopsy with blue dye which is the standard procedure for axillary staging in early breast cancer.

Twenty-five percent of patients undergoing SLN biopsy currently require a second operation. This study looked at whether identification of SLNs with microbubbles would prevent or reduce the need for second operation.

“In order to validate our results with surgical results, we inserted a guide-wire into the enhancing lymph node preoperatively and correlated these nodes with the surgeons ‘hot’ and blue nodes. We showed that what we saw was the same as what a surgeon would have otherwise seen,” Sever said.

Following the successful validation phase they recruited 99 patients with proven invasive breast cancer who received microbubbles injected intradermally into the areola margin. SLNs were identified and biopsied preoperatively by contrast-enhanced ultrasonography.

Depending on the biopsy results, patients had either a conventional SLN biopsy or axillary lymph node dissection (ALND). In 97 cases, SLN was successfully identified. Eighteen of these were lymph node positive. Eleven of this group were proven node positive by using the microbubbles and were treated with immediate ALND whilst the remainder underwent conventional SLN biopsy with blue dye and isotope injection. “We reduced futile SLN procedures to 8 percent due to this microbubble procedure,” Sever said.

In conclusion, Sever said that microbubbles can identify the SLN, and when the enhanced lymph node is biopsied it is possible to reduce the completion ALND rates in more than 50 percent of the cases, however a negative biopsy result cannot omit the need of a conventional SLN biopsy.