Mapping of occult melanoma micrometastases in the inguinal lymph node basin by immunohistochemistry and RT-PCR.

ABSTRACT

To examine the distribution of occult micrometastases that could be potential sources of recurrence, complete maps of microscopic and submicroscopic metastases in entire inguinal lymph node basins were generated in 13 melanoma patients who had undergone elective or therapeutic lymphadenectomy. Occult micrometastases were analysed immunohistochemically for the pigment cell-specific antigen HMB-45 in all 155 nodes and using a reverse transcriptase-polymerase chain reaction (RT-PCR) assay to detect tyrosinase mRNA in 35 nodes. Five patients were determined to be node-negative by routine histopathology; three of these subjects were also negative by RT-PCR and/or immunohistochemistry. However, the remaining two patients had occult metastases, which were confined to a possibly sentinel node in one and were detected in multiple nodes in the other. Eight patients had histological evidence of lymph node metastasis. Three of these patients had no additional detectable submicroscopic disease, and one had occult metastasis in one node adjacent to the histologically positive node. In contrast, the other four patients had occult micrometastases in multiple non-sentinel, higher level nodes. The two patients who relapsed belonged to this group. The results show considerable variation in the distribution pattern of occult metastases in the regional lymph nodes, and have significant implications for the role of regional lymph node dissection, including sentinel node mapping with selective lymphadenectomy, in the management of melanoma patients.