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 w ith cutaneous melanomas. The detection of tyrosinase mRNA in melanoma SLN s pecimens by reverse transcription-polymerase chain reaction (RT-PCR) has be en reported to be a more sensitive method to detect subclinical metastases, compared with histological analysis. The aims of this study were to (1) de fine the yield of RT-PCR in assessing SLNs, compared with histological anal ysis, (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 underwen t SLN biopsy (between October 1996 and March 1997). One half of each SLN wa s 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 wi thout 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 pati ents exhibited melanoma metastases in routine histological examinations. Al l 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-posi tive. Conclusions: Among patients undergoing SLN biopsy, tyrosinase mRNA was dete ctable in 73% of SLNs from patients at risk for regional nodal metastases, including all of those with histologically positive SLNs. There is a defina ble 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 assa y.