Detection of Occult Melanoma Cells in Paraffin-Embedded Histologically Negative Sentinel Lymph Nodes Using a Reverse Transcriptase Polymerase Chain Reaction Assay

Abstract

PURPOSE: Detection of occult metastasis before the development of clinical disease could allow more accurate staging, appropriate follow-up procedures, and adjuvant therapies in patients with malignant melanoma (MM). The sentinel lymph node (SLN) has been proposed as a reliable predictor of metastatic disease in the lymphatic basin draining the primary melanoma. In this study, we screened both paraffin-embedded SLNs and peripheral-blood (PB) samples from MM patients at various stage of disease using a multimarker reverse transcriptase polymerase chain reaction (RT-PCR) assay. The prognostic significance of the presence of PCR-positive markers was also evaluated. PATIENTS AND METHODS: Total RNA was obtained from paraffin-embedded SLN sections and PB samples of 75 MM patients. RT-PCR was performed using tyrosinase and MelanA/MART1 as melanoma-associated markers. Radiolabeled PCR products were analyzed on denaturing polyacrylamide gels. RESULTS: Good sensitivity of the RT-PCR assay on archival tissues was demonstrated after comparison of RT-PCR results on frozen and paraffin-embedded SLNs from 16 MM patients. Significant correlation between the disease stage and marker expression in both PB and SLN samples was observed; the highest value was for patients who were positive for both markers in SLN (P = .006). Progression of disease was significantly associated with the total number of PCR-positive markers in both PB (P = .034) and SLN (P = .001) samples. CONCLUSION: Although sensitivity is lowered by the use of paraffin-embedded specimens, our data indicate that RT-PCR analysis of serial sections from archival SLNs may be helpful in improving detection of occult micrometastases, thus improving staging of patients with melanoma.