Polymerase chain reaction-based detection of circulating melanoma cells as an effective marker of tumor progression

Purpose: Reverse transcriptase (RT) polymerase chain reaction (PCR) with multiple markers has been demonstrated to be highly sensitive in detecting circulating cells from patients with malignant melanoma (MM). We evaluated the clinical significance of the presence in peripheral blood of specific PCR-positive mRNA markers as an expression of circulating melanoma cells. Patients and Methods: Total cellular RNA was obtained from the peripheral blood of 235 patients with either localized (n = 154) or metastatic (n = 81) melanoma. We performed RT-PCR using tyrosinase, p97, MUC18, and MelanA/MART1 as gene markers. The PCR products were analyzed by gel electrophoresis and Southern blot hybridization. In addition, 20 healthy subjects and 21 patients with nonmelanoma cancer were used as negative controls. Results: Although detected at various levels among assessable patients, each mRNA marker was significantly correlated with disease stage. A significant correlation with disease stage was demonstrated for patients who were positive to all four markers (P <.0001) or to at least three markers (P <.001). Univariate analysis showed a significant correlation between risk of recurrence (evaluated in stage I, II, and III patients) and increasing number of PCR- positive markers (P = .0002). Logistic regression multivariate analysis indicated that each single marker (except tyrosinase) and, more especially, the presence of four PCR-positive markers remained statistically independent prognostic factors for tumor progression. Conclusion: Our data establish the existence of a significant correlation among clinical stages, tumor progression, and presence of circulating melanoma-associated antigens in peripheral blood of MM patients. Preliminary assessment of a subset of patients with a higher risk of recurrence needs longer follow-up and further studies to define the role of RT-PCR in monitoring MM patients.