Despite the acceptance of sentinel node biopsy as a standard of care for melanoma staging, the procedure is not likely to be offered at every community hospital in the United States in the future because it is technically demanding and its success depends directly on the surgeon’s skill, particularly for head and neck cancers. The learning curve is steep and requires 30 to 50 surgeries for a surgeon to become proficient, Dr. Morton and others agree. In the recent international trial, surgeons were required to have performed 30 sentinel node biopsies before they could enroll patients. Even so, the false-negative rate in the trial was 3.4%, whereas Dr. Morton’s own false-negative rate is 1.5%. We have shown in another paper that it is purely experience-driven. The greater the volume of patients a center has, the lower their false-negative rate, Dr. Morton said.
Explore This IssueJuly 2007
To identify a sentinel node, the surgeon injects the site of the primary tumor with a mixture of blue dye-often isosulfan blue-and a radioactive isotope, usually technetium-99m bound to sulfur colloid. The surgeon and a nuclear medicine specialist then use a handheld gamma counter to identify the hot spot on the skin; if lymphoscintigraphy is used to image the region, the lymphatic channel can often be identified. Once the surgeon has localized the sentinel node or nodes on the skin, he or she can open up the region, bearing in mind that if the node is positive the surgeon will likely use the same incision site to remove the remaining nodes. The lymphatic channel and sentinel node will appear blue due to the presence of the dye. To ensure that all the sentinel nodes have been identified, the removed nodes should be held up to a gamma counter to ensure that the majority of the radiation is accounted for. Surgeons will often remove any additional nodes that contain as much as 10% of the radioactivity in the hottest node.
Once the sentinel node is removed it can be sectioned and stained with standard H&E staining and with immunohistochemistry for disease-specific markers. Because the pathologist is examining only a few nodes rather than all of the nodes in a basin, the nodes can be analyzed more intensively, and smaller micrometastases identified if present.
Unlike the axilla or groin, which have relatively simple lymphatic drainage patterns, the neck region is complex. To illustrate that point, Dr. Morton noted that although surgeons were able to identify sentinel nodes in 99% of the axilla and groin lymph basins in the trial, they succeeded in finding sentinel nodes in only 84% of basins in the neck. Moreover, whereas 70% of the time there are only one or two sentinel nodes in the axilla and groin, the neck region frequently has more than two. I’ve seen up to six sentinel nodes, Dr. Morton said. Because the drainage is so complex, there are more likely to be multiple sentinel nodes, and therefore surgeons are more likely to miss one.