Collectively, we have demonstrated that (1) Dicer knockdown in melanoma decreased tumor progression and extended overall survival of mice; (2) melanoma cells with Dicer knockdown induced an anti-tumor immune response; (3) control of Dicer knockdown melanoma tumors was dependent upon an intact immune system, especially CD8+ T cells; and (4) melanoma cell over-expression of Dicer weakened CD8+ T cell recognition/killing. This evidence concerns the gene DICER1 and neoplasm.