Abstract Melanoma is the deadliest form of skin cancer, and the incidence of melanoma has been rising for the last 40 years. There is a paucity of readily available tools to predict for melanoma progression and response to therapy, leaving an unmet medical need to identify predictive and prognostic biomarkers. Doublecortin-like kinase 1 (DCLK1) is overexpressed and marks a population of tumor-initiating cells in colonic and pancreatic cancers. It regulates key oncogenes, pluripotency factors, angiogenic factors, and epithelial mesenchymal transition (EMT) related transcription factors. In this study, we evaluated whether DCLK1 can be detected in the bloodstream and if its levels in serum samples could be quantitatively assessed in melanoma patients. ELISA assay was performed to detect DCLK1 levels in the serum samples of melanoma patients before and after treatment with either targeted agents or immune checkpoint inhibitors. Western blotting was also performed to detect DCLK1 protein in the serum samples of melanoma patients. Immunohistochemistry (IHC) analysis was performed to detect DCLK1 in the same patients' tumor tissues. Additionally, analysis of DCLK1 and correlative gene expression profiles was performed using TCGA Melanoma dataset. Here we report that the intensity of DCLK1 staining in melanoma tumor tissues is increased compared to normal tissues. DCLK1 levels in the serum were elevated in melanoma patients (n=20) compared to healthy volunteers. Next, we compared DCLK1 levels in 10 patients for whom pre- and post- treatment samples were available. Among these patients, seven had elevated DCLK1 before treatment and had a significant decrease (about 30-50%) in serum DCLK after treatment. Three patients had no change in DCLK1 levels after treatment. The patients with a decrease in their level of DCLK1 post-treatment demonstrated radiologic response to therapy as well, while the patients with no change in DCLK1 level post therapy showed either no improvement or progression (p<0.002). These data suggest that reduction in serum DCLK1 levels following therapy for melanoma was associated with clinical response, and the absence of change in DCLK1 after therapy was associated with poor response. Analysis of the TCGA dataset demonstrated that melanoma patients with high levels of DCLK1 had worse overall survival (p<0.05) compared to the patients with low levels of DCLK1, suggesting that DCLK1 RNA levels could be used as a prognostic biomarker. These data taken together suggest that DCLK1 has potential utility as a novel predictive and on-treatment biomarker for melanoma prognosis and therapeutic response. Citation Format: Dongfeng Qu, Nathaniel Weygant, Parthasarathy Chandrakesan, Kamille Pitts, Randal May, Sripathi Sureban, Adam Asch, Alexandra Ikeguchi, Courtney Houchen. Serum DCLK1 levels are elevated in melanoma patients and it is a novel predictive marker for survival and response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3611.