Detection of tumor-associated circulating mRNA in serum, plasma and blood cells from patients with disseminated malignant melanoma.

Reverse transcription polymerase chain reaction (RT-PCR)-based detection of tyrosinase mRNA is a frequently used method for the identification of circulating tumor cells in melanoma patients. The significance and practical value of this procedure for the diagnosis of tumor dissemination in melanoma patients are unclear. The conflicting results may at least partially be related to very low amounts of circulating tumor cells and to our observation that melanoma cells only transiently persist in the peripheral blood. The purpose of the present study was to evaluate the relevance of detection of extracellular melanoma-specific mRNA in serum and plasma samples in comparison to blood cell samples from patients with disseminated disease (stage IV). We therefore compared the presence of specific mRNA for tyrosinase, gp100, and MART-1 by RT-PCR amplification of specific cDNA from serum, plasma, and whole blood samples of 10 melanoma patients. Melanoma-specific mRNA was detectable in whole blood samples of all ten patients tested indicating the presence of circulating melanoma cells. In addition, tyrosinase mRNA could be detected in the serum and/or plasma of 6 of 10 melanoma patients whereas gp100 and MART-1 specific transcripts were not detectable in any of the samples tested. The presence and integrity of amplifiable RNA was shown in all serum and plasma samples of patients and controls by RT-PCR-specific amplification of porphobilinogen deaminase (PBDG) mRNA. We conclude that tyrosinase mRNA but not gp100 and MART-1 mRNA can be amplified from serum and/or plasma in a subset of melanoma patients showing circulating melanoma cells. Therefore, extracellular-directed assays appear to be less sensitive and efficacious in detecting melanoma-specific transcripts compared to cellular-based assays.