RESUMO
The presence of tyrosinase mRNA in the peripheral blood cells of melanoma patients has been recently studied as a possible marker of haematogenous dissemination. However, considerable variations in the rates of detection have been noted. We determined the presence of tyrosinase mRNA-positive circulating cells using reverse transcriptase-polymerase chain reaction (RT-PCR) in 35 patients with stage I melanoma, two patients with stage II melanoma and two patients with stage III melanoma. Among the patients with stage 1, 13 were tested before and after surgery (< 1 h). Twenty healthy subjects served as negative controls. Out of the melanoma patients, the tyrosinase gene was expressed in three of the 52 samples tested. Tyrosinase mRNA was present in the circulating cells of only one patient with stage I melanoma after intra-congenital naevi resection. However, two other stage I patients developed rapidly lethal metastasis within the following 6 months, despite the lack of detectable tyrosinase mRNA. None of stage II patients were positive for the tyrosinase transcripts, while both patients with stage III melanoma showed enzyme expression. Our results confirm those of previous studies, showing that a small proportion of stage I melanoma patients have tyrosinase-positive circulating cells. Moreover, the lack of tyrosinase mRNA detection in the blood does not necessarily exclude metastatic progression. Therefore, this study indicates that the detection of tyrosinase mRNA-positive circulating cells by RT-PCR is not a predictive biomarker of a metastasis risk in patients with stage I melanoma.
