Detection of Melanoma Micrometastasis in Sentinel Nodes by Reverse Transcription-Polymerase Chain Reaction Correlates With Tumor Thickness and Is Predictive of Micrometastatic Disease in the Lymph Node Basin

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Abstract
The sentinel node has been reported to be representative for the presence or absence of metastatic melanoma in the draining lymph node basin. In this study, for the first time sentinel nodes and adjoining nonsentinel nodes were analyzed for micrometastatic disease using tyrosinase reverse transcription-polymerase chain reaction (RT-PCR) in comparison with standard immunohistochemistry. Successful identification of the sentinel nodes using a gamma probe–guided surgery was achieved in 73 (92%) of 79 patients with cutaneous stage I and II melanoma (tumor thickness ≥0.75 mm). A total of 794 regional lymph nodes, 148 sentinel nodes, and 646 adjoining nonsentinel nodes were evaluated. Tyrosinase RT-PCR was shown to increase the sensitivity for melanoma cell detection in sentinel nodes significantly (49% positivity) as compared with immunohistochemistry using antibodies against HMB-45 antigen and S-100 protein (18% positivity). Examination of sentinel nodes was highly predictive in determining the presence of regional lymph node micrometastasis by immunohistochemistry (99%) and RT-PCR (89%). Interestingly, detection of nodal micrometastasis by RT-PCR showed a strong positive correlation with tumor thickness of primary cutaneous melanoma. These results suggest the clinical significance and emphasize the importance of tyrosinase RT-PCR for detection of melanoma micrometastasis in sentinel nodes.