Lymphatic system mapping is becoming more sophisticated, with new imaging strategies and tools that are moving sentinel lymph node (SLN) detection beyond the inexact two-dimensional structural imaging of node size and shape, to more precise, three-dimensional imaging modalities and the physiological differentiation of SLNs from other lymphatic tissues.

Newly approved by the Food and Drug Administration (FDA), radiolabeled SLN imaging agent, Lymphoseek® (technetium Tc-99m tilmanocept) Injection is the first approved receptor targeted agent. It promises to help reduce unnecessary lymph node biopsies—and hopefully associated morbidities, like lymphedema—by identifying nodes that are most likely to contain tumor cells.

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Detecting cancer cells’ presence in lymph nodes is a key step in the accurate staging of several types of solid tumor cancers, and also helps to inform prognosis as well as plan appropriate treatment. The lymphatic system is frequently a route of primary tumor metastasis to distant organs; therefore, mapping lymphatic drainage to the lymph nodes nearest to a primary tumor—the sentinel lymph nodes(SLNs)—for node biopsy plays an important role in determining whether or not the spread of tumor cells has begun. SLNs represent the lymph nodes to which metastatic cells first escape, and harbor tumor cells earlier than other, more distant lymph nodes.

SLN mapping and biopsy has become a routine procedure for melanoma patients, notes Vernon Sondak, MD, chair of the Department of Cutaneous Oncology at the Moffitt Cancer Center in Tampa, FL. 

“Most patients present with clinically localized disease, but microscopic metastases to the regional lymph nodes are common and are the major prognostic factor for these patients,” Sondak said.

While lymphatic mapping is not well standardized around the world, it can be performed both preoperatively and intraoperatively, using different imaging agents and detection or imaging modalities, Dr. Sondak and other experts told

Traditional strategies in the United States include intraoperative injection of blue dyes near the primary tumor (which drain into sentinel lymph nodes to allow their visual detection during surgery) and preoperative or intraoperative lymphoscintigraphy with radiolabeled sulfur colloids. Blue dyes tend to diffuse quickly through the lymphatic system to reach SLNs within a few minutes, whereas radiolabeled colloids tend to diffuse more slowly but are retained for longer periods in lymphatic tissues. Because radiocolloids do not accumulate differentially in SLNs, however, they can in some cases poorly differentiate SLNs from other lymph nodes.