Many patients who exhibit a response to the anti-PD-1 antibodies develop a prolonged course of disease stability which resembles the equilibrium phase of the previously proposed process of cancer immunoediting. This state of equipoise has been hypothesized to involve genetic alterations that promote immune evasion and, in some cases, lead to the development of tumor escape. Based on our data, the investigators propose that melanomas that develop a period of disease stability in response to anti-PD-1 immunotherapy exhibit genetic alterations that suppress the effectiveness of anti-tumor immunity. Our previous studies indicate that the tumor-derived factors that play a role in the paracrine signaling pathways capable of regulating nearby stromal cell populations are more likely to be critical immune regulators of the tumor microenvironment. Therefore, the investigators will focus our studies on those differentially expressed genes which encode soluble proteins using an available prediction algorithm. Those genes identified by this study to be differentially expressed in the melanoma tissues of patients demonstrating a clinical response to immune checkpoint inhibitor therapy will be further evaluated in transgenic autochthonous melanoma models.