Removal of Low-Radioactivity Sentinel Lymph Nodes Recommended

A new study suggests that multiple lymphatic channels may exist, draining into more than one sentinel lymph node (SNL), and recommends that SLNs with low radioactivity should also be removed to ensure complete resection.

Researchers from the University of California San Francisco (USA) sought to validate the "10% rule” hypothesis, which states that while the hottest SLN has the highest likelihood of harboring tumor cells, all nodes with more than 10% of the ex vivo radioactive count of the hottest SLN should be removed. The researchers found that among 332 primary breast cancer patients who underwent sentinel lymphadenectomy, the radioactivity of the positive nodes apart from the hottest node ranged between 0.8% and 90% of the counts of the hottest lymph node, but only 6.5% of radioactive nodes had less than 10% of the radioactivity of the hottest lymph node. Only nine lymph nodes (15%) with radioactive counts less than 10% of the hottest lymph node were found to harbor tumor cells, with the lowest radioactivity of a node positive for cancer reaching 4.2% of the radioactivity of the hottest node. The researchers found that if only the hottest node was removed, the false-negative rate was 14.1% and the accuracy 96.7%; but if the 10% rule was applied, the false-negative rate dropped to 6.4% and accuracy increased to 98.5%. The study was published in the December 2008 issue of the Journal of the American College of Surgeons.

"These findings indicate that there is more than one sentinel lymph node, suggesting that more than one lymphatic channel can lead the cancer cells to one or more sentinel lymph nodes,” said lead author Stanley Leong. M.D. "In order to reduce the false-negative rate, the surgeon needs to take out not only the hottest lymph node but also additional ones, as low as to, [or] at least, 10% of the hottest lymph node.”

Prior to sentinel lymph node biopsy, the surgeon injects a small dose of a low-level radioactive tracer called technetium-99 into the breast in the region of the patient's tumor. A blue dye is also injected to help visually track the location of the sentinel node during surgery. Depending on the protocol followed, the surgeon usually waits between 45 minutes to 8 hours after injection before bringing the patient to the operating room for the biopsy. Once the technetium-99 tracer and dye have reached the nodes, the surgeon scans the area with a hand-held Geiger gamma ray counter attached to a probe used to trace the SNLs. When the radioactive agent is found, the gamma ray counter will emit an audible tone, revealing the exact location of the sentinel node(s). The blue dye provides additional visual confirmation of the sentinel node's location during surgical removal.

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