Detection of tyrosinase mRNA by reverse transcription-polymerase chain reaction in melanoma sentinel nodes

Background: Sentinel lymph node (SLN) biopsy is an alternative to elective dissection or observation for management of lymph node basins in patients with cutaneous melanomas. The detection of tyrosinase mRNA in melanoma SLN specimens by reverse transcription-polymerase chain reaction (RT-PCR) has been reported to be a more sensitive method to detect subclinical metastases, compared with histological analysis. The aims of this study were to (1) define the yield of RT-PCR in assessing SLNs, compared with histological analysis, (2) identify the incidence of false-positive results in SLNs, and (3) report the rate of actin PCR negativity (i.e., samples with degraded RNA) in SLNs. Methods: Twenty-eight patients with 1.2-9.6-mm cutaneous melanomas underwent SLN biopsy (between October 1996 and March 1997). One half of each SLN was analyzed by nested RT-PCR for tyrosinase mRNA. The other half of the SLN was examined by routine microscopy. Twenty-one lymph nodes from patients without melanoma were evaluated as controls. Results: Two of the 28 patients with melanoma were excluded because of RNA degradation, as indicated by actin negativity. Six of the remaining 26 patients exhibited melanoma metastases in routine histological examinations. All histologically positive lymph nodes were RT-PCR-positive. Thirteen of the 20 (65%) histologically negative cases were RT-PCR-positive. Of 21 control lymph nodes, 3 were actin-negative and were not assessable for tyrosinase mRNA. Two of the remaining 18 (11%) negative-control nodes were RT-PCR-positive. Conclusions: Among patients undergoing SLN biopsy, tyrosinase mRNA was detectable in 73% of SLNs from patients at risk for regional nodal metastases, including all of those with histologically positive SLNs. There is a definable false-positive rate for tyrosinase mRNA detection in the lymph nodes of patients who do not have melanoma. Actin verification of RNA integrity is necessary to ensure the accuracy of this test in detecting tyrosinase mRNA. Ongoing follow-up monitoring will define the prognostic value of this assay.