Probabilistic Issues With Sentinel Lymph Nodes in Malignant Melanoma

Abstract

Objectives: To address issues of probability for sentinel lymph node results in melanoma and provide details about the probabilistic nature of the numbers of sentinel nodes as well as to address how these issues relate to tumor thickness and patient outcomes. MethodsAlthough the therapeutic benefit of sentinel lymph biopsy in melanoma remains controversial, sentinel lymph nodes clearly provide prognostic information. 1-3 In addition, it is clear that detecting metastases in sentinel lymph nodes depends on how many nodes are found as well as on how much histologic effort is made. For example, removal of fewer than three sentinel nodes implies greater tumor recurrence, 4-6 as well as less accurate assessment of the total number of positive sentinel lymph nodes, a proven prognosticator. 7,8 Regarding histopathologic effort, many have shown that more slides and immunohistochemical stains yield more positive nodes. 9-14 Thus, fewer sentinel nodes and fewer sections may yield false-negative results. Bahmer underscored the probabilistic nature of sentinel node results when he wrote, "The chance to detect a micrometastasis is proportional to the number of specimens investigated. Even in a very elaborate investigation with many slides prepared, there is still a considerable risk to miss tiny metastases." 15 In addition, Medalie and Ackerman addressed "the randomness of the process of metastasis," which they said was "manifest in the finding of metastases in some patients in whom no melanoma cells were detected in a SN [sentinel node]." 16 In this report, I address probabilistic issues for sentinel lymph node results in melanoma and provide new details about the probabilities of numbers of sentinel nodes-positive as well as total-and then address how this model relates to tumor thickness as well as to patient outcomes.