Project Summary The incidence of thyroid cancer is rapidly increasing in the US and is projected to surpass colorectal cancer as the 4th leading cancer diagnosis by 2030. The majority of patients respond to initial therapy, but approximately 20% will develop recurrence and 10% will develop metastatic disease. Treatment options are extremely limited for patients with metastatic, recurrent, or poorly-differentiated disease, such as anaplastic thyroid carcinoma (ATC). ATCs usually carry common driver mutations, such as BRAFV600E, but BRAF inhibitors have shown limited efficacy in the treatment of ATC. Interestingly, the majority of ATC have also been found to exhibit increased Wnt activity, and Wnt has been shown to mediate BRAF-inhibitor resistance in other cancer types. Wnt has also been shown to contribute to aggressive tumor behavior through the development of an immunosuppressive tumor microenvironment. The goal of my proposal is to define the role of Wnt in tumor progression and therapeutic resistance in anaplastic thyroid cancer. My preliminary work in the development of novel spheroid and organoid culture systems provides a unique opportunity to analyze the effects of Wnt inhibitors in a near-in vivo system derived from primary patient samples. In this proposal, I will test the hypothesis that Wnt signaling in the tumor and tumor microenvironment drive disease progression and therapeutic resistance in aggressive thyroid cancers. In Aim 1, I will define the molecular interaction between the Wnt and MAPK signaling pathways that enable resistance to BRAF inhibitors and examine the potential utility of Wnt inhibitors in the treatment of BRAF-inhibitor resistant and aggressive disease. In Aim 2, I will elucidate the role of Wnt in the development of an immunosuppressive tumor microenvironment and investigate the immunomodulatory properties of Wnt inhibitors in vivo utilizing a humanized tumor xenograft murine model and in vitro using monocyte-tumor spheroid co-cultures, both of which I have developed for this project. In completing these studies, I will delineate the contributions of Wnt in BRAF-inhibitor resistance and immunomodulation in aggressive thyroid cancer in order to characterize a therapeutic target in a disease with limited treatment options.