ABSTRACT Cell migration is important in normal development, wound healing and cancer. The long-term goal of this work is to study cell migration in the context of cancer. The most motile, and understudied, population of cells in the tumor microenvironment (TME) are neutrophils, which are primary effector cells of the innate immune response. The presence of chronic neutrophil- mediated inflammation has been associated with the initiation and progression of cancer. However, the role of neutrophils in the tumor microenvironment remains controversial in part because neutrophils can play both pro- and anti-tumor roles. We aim to address this gap by increasing our understanding of how neutrophils are recruited and regulated by the tumor microenvironment during tumor progression. We will test the overall hypotheses that specific signaling pathways induced by transformed cells drive neutrophil recruitment, and that neutrophils “educated” in the tumor microenvironment alter tumor progression. To address these hypotheses, we have developed a robust toolbox using zebrafish to enable in situ imaging of the dynamic behavior of neutrophils, macrophages and cancer cells, in real time, in melanoma and liver cancer models. We take advantage of a new zebrafish model of fibrolamellar carcinoma (FLC), an aggressive early onset cancer that exhibits increased inflammation and early progression, similar to human disease. Here, we propose to examine the role of neutrophils in liver cancer and melanoma inflammation and progression (Aim 1). We will harness TRAPseq findings from neutrophils, macrophages and epithelial cells to probe the role of oncogene-induced genes on neutrophils in the tumor microenvironment and tumorigenesis, including the role of neutrophil intrinsic genes p47phox and the phosphatase ptprja on neutrophil polarization and tumor progression (Aim 2). Finally, we will examine neutrophil-macrophage cross talk in the tumor microenvironment and the role of macrophage polarization on neutrophil inflammation and tumor progression (Aim 3). While there has been substantial interest in manipulating the adaptive immune system to treat cancer, the therapeutic possibilities of the innate immune system remain under-studied. Understanding mechanisms that regulate neutrophils in the tumor microenvironment will enhance basic mechanistic knowledge regarding intercellular interactions, facilitate the design of new strategies to treat cancer and potentially improve the efficacy of cancer immunotherapy.