PERIPHERAL-BLOOD TYROSINASE MESSENGER-RNA DETECTION AND SURVIVAL IN MALIGNANT-MELANOMA

Background: The most widely accepted criteria for the evaluation of pr ognosis of malignant melanoma are histopathologic and clinical present ation. No currently available laboratory tests provide additional prog nostic information. It has recently been suggested that reverse transc ription and polymerase chain reaction (RT-PCR)-based detection of tyro sinase messenger RNA (mRNA) in peripheral blood might be useful in the early detection of circulating tumor cells, since tyrosinase is thoug ht to be a melanocyte-specific marker. Purpose: To further evaluate th e clinical relevance of this potential marker, we examined peripheral blood samples from patients with malignant melanoma in different stage s of disease for the presence of tyrosinase mRNA. Methods: Total cellu lar RNA was extracted from heparinized peripheral blood cells from 64 patients with malignant melanoma, from five healthy control subjects, and from four patients with other cancers using the RNAzol A method. F or analysis of tyrosinase mRNA, RT-PCR was performed as previously des cribed by Smith et al.; the sensitivity of this assay was tested using RNA extracted from human melanoma cells (SK-mel 1 and SK-mel 3 cell l ines) serially diluted with peripheral blood obtained from healthy con trol subjects. Two additional human melanoma cell lines (SK-mel 30 and RPMI-7951) served as positive controls for RT-PCR detection of tyrosi nase mRNA. Overall patient survival curves were constructed using Kapl an-Meier estimates. Results: Tyrosinase mRNA was detected by RT-PCR as say of all four of the established melanoma cell lines tested. Nine of the 64 patients with malignant melanoma were found to have detectable tyrosinase mRNA in their peripheral blood cells (tyrosinase-positive patients). The 16 patients with localized primary melanoma did not hav e detectable tyrosinase mRNA in their peripheral blood cells. Among th e 48 patients with metastatic disease, all 27 patients who exhibited n o evidence of disease progression were tyrosinase negative. Notably, a ll nine tyrosinase-positive patients had visceral metastases and were found to exhibit disease progression at the time of the sampling. Four of the nine tyrosinase-positive patients were also found to test nega tive at times without evidence of progressive disease; one patient bec ame negative after achieving stable disease and three became positive for tyrosinase transcripts on disease progression. The probability of survival from time of sampling was significantly lower in the nine tyr osinase-positive patients when tested versus the 23 patients with comp arable disease but without detectable tyrosinase mRNA (two-sided; P le ss than or equal to .05). Conclusions: The results of this study demon strate that the tyrosinase mRNA in peripheral blood by RT-PCR may be a useful prognostic marker for predicting tumor progression and poor cl inical outcome in patients with malignant melanoma.