Lymphedema is an incurable condition characterized by lymphatic obstruction, tissue swelling, immune dysfunction, and fibrosis after lymphatic injury. Lymphedema affects 5 million Americans and is associated with poor quality of life due to extremity disability, disfigurement, and risk for recurrent limb-threatening infection. In the US, lymphedema is most commonly a consequence of lymph node dissection for the treatment of solid tumors such as breast or pelvic cancer. Despite the fact that lymphedema is common and morbid, there are currently no effective drug treatments. Using preclinical rodent models of lymphedema, we have shown that 9-cis retinoic acid (RA) significantly accelerates lymphatic regeneration following injury, restores functional lymphatic drainage, and prevents development of lymphedema. Our overarching hypothesis is that RA-mediated lymphangiogenesis is a promising therapy for secondary lymphedema. The objective of this proposal, which is the first logical step towards implementing this treatment clinically, is to increase our understanding of the mechanisms by which RAs regulate lymphangiogenesis and develop a translational framework for the use of these compounds. The specific aims of this proposal include Aim 1: Determine how RA selectively induces lymphangiogenesis; Aim 2: Elucidate the roles of FGFR and VEGFR signaling in RA-mediated lymphangiogenesis; and Aim 3: Use early biomarkers of lymphatic insufficiency to develop a predictive model that can guide initiation of RA therapy. Based on the current lack of effective therapy, it is clear that there is a need to develop an etiology-focused treatment for post-surgical lymphedema. The proposed studies will address important mechanistic questions regarding RA mediated lymphangiogenesis and also develop an early biomarker based predictive model that will guide treatment windows for RA therapy. The proposed work will significantly improve our understanding of RA-mediated lymphangiogenesis as well as support clinical translation of a RA as a preventative treatment regimen for post-surgical lymphedema.