Purpose: Metastatic uveal melanoma is resistant to conventional chemotherapy and immunotherapy. In this study, we investigated the responsiveness of uveal melanoma cell lines to IFNs and the hypomethylating agent decitabine. Experimental Design: The uveal melanoma cell lines 92-1, UW-1, OCM-1, and MKT-BR were exposed to varying concentrations of IFN-a, IFN-g, and decitabine, alone and in combination. The effects of decitabine on gene expression were examined using DNA microarray analysis. Results: We found that IFN-g and decitabine induced cell death in uveal melanoma. Whereas a high concentration of IFN-g (1,000 units/mL) was required to induce cell death, we observed a dose-related increase in cell death when decitabine was used at a range of 0.1 to 10 Amol/L. Strikingly, 1 Amol/L decitabine synergized with 10 to 1,000 units/mL IFN-g to induce massive cell death. In contrast, decitabine had no effect on three cutaneous melanoma cell lines and exhibited no synergy with either IFN. In uveal melanoma, decitabine up-regulated the expression of genes involved in growth control and apoptosis and down-regulated genes that have been implicated in the malignant phenotype of cutaneous melanoma. The gene up-regulated to the greatest degree by decitabine and whose expression showed a dose-effect across the three concentrations of decitabine was S100A2, a putative tumor suppressor.The genes modulated by decitabine in uveal melanoma were largely unaffected in cutaneous melanoma. Conclusions: These findings form a basis for testing the decitabine/IFN-g combination in metastatic uveal melanoma and for exploring the role of S100A2 in the susceptibility of uveal melanoma to IFN-mediated cell death.Metastatic uveal melanoma is an aggressive malignancy with a median survival of <6 months (1). Patients with locally advanced primary lesions also have a poor prognosis because up to 50% will subsequently develop disseminated metastases within 10 years (2). Although hepatic metastases can respond partially to intra-arterial chemotherapy or chemoembolization, metastatic uveal melanoma is largely resistant to systemic chemotherapy (3). Immunomodulatory drugs used to treat advanced cutaneous melanoma, including interleukin 2 (IL-2) and IFN-a, have also had very limited activity in uveal melanoma (4).The mechanism underlying the antitumor effect of IFN-a or IL-2 in select patients with advanced cutaneous melanoma remains poorly defined. The association of good outcome with the development of autoimmune breakthrough events (5,6) suggests that overcoming tolerance to self-antigens plays a role in cytokine-mediated antitumor immunity. However, IFN-a and IFN-g can also exert direct antiproliferative and/or proapoptotic effects on cutaneous melanoma cell lines (7, 8), illustrating how certain cytokines can have antitumor effects that are independent of the induction of antigen-specific cellular or humoral immunity.The epigenetic suppression of gene expression through DNA methylation has been linked to the relative resistance of a cuta...