Thyroid Tumorigenesis is typically a well understood process, with well delineated oncogenic factors. Follicular and papillary thyroid cancers are typically survivable, with 5-year survival rates being >95% for Stage I-III of both cancer types. Anaplastic thyroid cancer, in contrast, lacks this prognosis, and is the most lethal of all endocrine-related cancers. The median survival time after a diagnosis is generally between 6-8 months, with a 5-year survival rate of <10%. Current treatment for anaplastic thyroid cancers routinely meet roadblocks, as resistance is quickly developed. Even non-discriminatory kinase inactivators, such as sorafenib, which are generally considered a drug of last resort, are unable to effect survival rates. As such, there is a clear need for further investigation of the causes of anaplastic thyroid cancer mechanisms. Previous work in the Carr lab revealed a novel regulatory pathway of an oncogene that is associated with several other endocrine-related cancers, as well as other non-endocrine-related cancers. Specifically, the Runt-related transcription factor 2 (Runx2) was found to be suppressed via direct binding of the thyroid hormone receptor beta 1 isoform (TRss1) to its proximal promotor. Runx2 was previously shown to be associated with increasing malignancy, with Runx2 occurring at low-levels in indolent cell lines, whilst occurring at high-levels in more malignant cell lines. TRss1, conversely, exhibited the opposite relationship. Endogenous levels of TRss1 were found to be high in indolent cell lines and were depleted in malignant cell lines. These findings were further confirmed via tissue microarrays. Restoration of TRss1 in malignant cell lines diminished Runx2 mRNA and protein levels, which was corroborated by evidence from electrophoretic mobility-shift assays, and chromatin immunoprecipitations that TRss1 was able to directly bind Runx2 promotor 1. Current studies have investigated the nuclear protein profile that associates with TRss1 to alter Runx2 transcription. Through EMSA-to-Mass Spectrometry methodologies, as well as novel DNA pulldown techniques, binding partners have been elucidated. Findings have also been confirmed via classical immunoprecipitations. Specifically, our findings show that TRss1 complexes with the brahma-related gene 1 (BRG1) protein, the nuclear co-repressor (NCOR), and BRG1-associated protein 60 (BAF60). BRG1 functions by preferentially recruiting histone deacetylases (HDAC), with BRG1 and the HDAC's acting to alter chromatin, and thus transcription. Future studies aim at examining whether other proteins complex with TRss1 to alter Runx2 transcription, and whether these complexes are altered in aggressive cell lines.