[The sentinel lymph node in melanoma: utilization of molecular biology (RT-PCR) to detect occult metastases]

Sentinel lymph node (SLN) analysis allows the detection of occult metastases in patients with melanoma. The use of serial sections and immunohistochemical investigations (ICH) increases the chance of identifying metastases. Nevertheless, detection of mRNA of the tyrosinase gene through reverse transcription-polymerase chain reaction (RT-PCR) is the most sensitive tool for detection of occult melanoma cells in SLN. From September 1999 to August 2001, in the Anatomic Pathology Unit of M. Bufalini Hospital of Cesena, 489 SLNs from 332 patients with primary melanoma in clinical stages I and II (according to AJCC) were examined. There were 66 (13.5%) SLNs and 58 (17.4%) cases with metastasis revealed by histology and ICH. A single case with metastatic SLN was found in patients with melanomas < or = 1 mm in thickness. The percentage of cases with metastases in SLN correlated with thickness of the primary melanoma (p < 0.0001). RT-PCR for tyrosinase was carried out in 448 SLNs from of 308 cases. Overall, the RT-PCR results were positive in 149 (48.4%) patients and in 169 SLNs (37.9%). RT-PCR results showed a strong positive correlation with tumor thickness of primary melanoma (p < 0.0001) and with the clinical stage (p < 0.0001). Of the RT-PCR-positive cases, 18 showed intracapsular aggregates of nevus cells. Besides the percentage of positive cases, once those with nevus aggregates were excluded, overall, the RT-PCR revealed the presence of tyrosinase mRNA in 34.5% of patients with negative histology and ICH. Ongoing monitoring is necessary to define the real prognostic implication of the presumed presence of occult melanoma deposits disclosed by RT-PCR in SLNs.