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LETTER TO THE EDITOR |
Division of Surgical Oncology, University of Louisville, James Graham Brown Cancer Center, Louisville, Kentucky
In the August issue of Annals of Surgical Oncology, Martin et al.1 describe the likelihood of finding positive sentinel lymph nodes (SLN) for breast cancer relative to the degree of radioactivity of the nodes. They conclude that "neither the presence of blue dye nor isotope count ratios of any particular threshold level consistently identified the positive SLN in all patients." They recommend "the removal of all nodes containing isotope regardless of the relative magnitude of counts." We believe that these conclusions are hardly useful to surgeons faced each day with the decision to remove or not remove that third or fourth mildly radioactive lymph node. However, we also believe strongly that the ability to detect that third or fourth node, when it exists, is what reduces the false-negative rate.2
The authors analyzed 2285 consecutive breast cancer patients who underwent SLN biopsy. Only 5% of patients (24 of 463) with positive nodes had a positive sentinel node that was less than 10% of the radioactive count of the "hottest node." Of these 24 patients, all but 3 had blue-stained sentinel nodes. It is recognized that the blue dye and radioactive colloid injection techniques provide complementary approaches to SLN identification.3 That is explained by the fact that sometimes one finds blue nodes that are not very hot, hot nodes that are not blue, or even mildly hot lymph nodes that are not blue—any can be the sole site of metastatic disease.
The authors cited the "10% rule" that we validated in the University of Louisville Breast Cancer Study.4 This rule was devised by analyzing the likelihood of finding false-negative results, and is equally applicable to SLN biopsy for melanoma.5 The 10% rule has been a very practical and useful method to determine which radioactive nodes should be removed and designated as sentinel nodes, even if they do not contain blue dye staining. However, this rule does not just incorporate the radioactive counts. The 10% rule is stated as follows: "Any lymph node that is blue, any lymph node that is the hottest lymph node, and any lymph node that is 10% or greater of the ex vivo radioactive count of the hottest node should be removed."4,5 Finally, any suspicious palpable nodes should be removed, as suggested by Martin et al.1
If this rule were actually applied to the data presented in this study by Martin et al., only 3 of 463 patients with positive lymph nodes would have had false-negative results, for a false-negative rate of 0.6%. Furthermore, only 3 patients of 2285, or 0.13% of patients overall, would have suffered a false-negative result. The 10% rule, applied appropriately to the data of Martin et al.,1 allows detection of the overwhelming majority of positive sentinel nodes.
In summary, the 10% rule has been validated for both breast cancer and melanoma patients in large multi-institutional studies. When applied to the large study of Martin et al.,1 it works equally well. The suggestion by Martin et al. that all radioactive lymph nodes should be removed would result in unnecessary removal of an inordinate number of lymph nodes, because some background radioactivity is always present in the second- and third-echelon nodes. Surgeons learning this technique need useful guidelines to provide the greatest likelihood of success. We believe that, at present, the 10% rule is a simple and accurate method that lets the surgeon know when to quit looking for additional sentinel nodes.
REFERENCES
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