If detected early melanoma is usually curable with surgery. However, melanomas are often detected at later stages after cancer cells have metastasized and survival rates for patients with metastatic disease are less than 15%. Furthermore, some thin melanomas, even when detected early, lead to mortality. What defines this difference in outcome is largely unknown and suggests a need for new markers that can predict a patient’s risk. Recently, the cellular microenvironment that surrounds a tumor has gained significant attention as a critical regulator of tumor progression, response to therapy and resistance. Effective therapies that specifically target immune suppression by tumor microenvironments have been developed; however, our understanding of the specific way in which these therapies work is incomplete. A better understanding of which parts of the microenvironment suppress immune responses will not only allow for better prediction of patient prognosis but may also help enhance a patient’s response to new immune-based therapies. Lymphatic vessel growth in melanoma is correlated with poor prognosis and enhanced metastasis to lymph nodes, however, until now lymphatic vessels were largely ignored as players in host anti-tumor immune responses. Our recent work demonstrates for the first time that lymphatic vessels are immune suppressive in tumor microenvironments and impair therapy. This proposal will test the hypothesis that lymphatic vessels directly contribute to immune suppression and suggests they may be a novel marker both for risk stratification in melanoma patients and as a novel therapeutic target.