Detection of circulating malignant cells by RT-PCR in long-term clinically disease-free I stage melanoma patients.

Recently, reverse transcriptase-polymerase chain reaction (RT-PCR) for the detection of circulating tumor cells has been suggested as a potential technique for staging cancer. In this report, 43 melanoma patients (including 4 in situ melanoma patients) were tested for tyrosinase mRNA in blood by RT-PCR. All patients had melanoma thinner than 1.5 mm (stage I). Circulating melanoma cells were detected in 8 (18.6%) out of 43 MM patients tested: 5 (16.1%) of 31 patients with melanoma thinner than 0.76 mm and 3 (42.8%) out of 7 patients with melanoma thicker than 0.76 mm. Moreover, in the tyrosinase-negative group we found only 4/31 patients (13%) with histologic signs of regression, but in the tyrosinase-positive group, 3 out of 8 patients (37.5%) showed, at histologic examination, signs of regression. At the time of this analysis all the patients enrolled (tyrosinase-negative and tyrosinase-positive ones) were free of disease, probably due to the short median time of follow-up after the inclusion in the study. The presence of regression is an important cause of melanoma understaging and the tyrosinase test could represent an effective tool in order to achieve a realistic staging in this subgroup of melanoma patients. Probably, maximum sensitivity of the diagnostic RT-PCR approach to monitor MM patients with either localized or advanced disease could be achieved by using additional markers expressed with high frequencies in melanoma. We propose that one such marker could be the sign of regression.