Abstract Introduction/Objective Anaplastic thyroid cancer (ATC) is an aggressive rare malignancy found in less than 2% of thyroid cancer patients. Its low occurrence rate presents challenges for collecting sufficiently large cohorts at a single institution, making statistical analysis about the disease’s spread, geographical distribution, and prevalence difficult. Nationwide data lakes such as Oracle EHR Real-World Data (ORWD, formerly Cerner Real World Data) offer a boost in cohort sizes and an opportunity to study ATC’s geographical distribution and assess regional differences. Methods/Case Report We searched ATC distribution across US regions defined by ZIP codes recorded in ORWD using multiple coding parameters, including ICD9, ICD10, and SNOMED as well as direct text searches for “anaplastic thyroid carcinoma”. We analyzed the geographical associations defined by ORWD (region) with sex, race, and age of ATC onset using the Fisher’s exact test. We combined 10 regions into 4 representative groups because of the small sample size. The groups are West Coast including the Rockies, Midwest from North Dakota to Texas, East Coast, and New England. Results (if a Case Study enter NA) Search for ATC condition codes in ORWD produced only 200 region-coded patient records across the US using multiple methods to try and identify cases. The mid-section of the US and coastal regions shows the highest numbers of ATC patients while New England and South regions show the lowest. While more women have ATC overall, the East Coast group has significantly more males (p value = 0.04). ATC is a predominantly white disease (79.8% overall) with black population increasing in East Coast group and other races (Asian/Undeclared) in West Coast (p-value < 0.001). There appears to be no significant association between age of ATC onset and the geographical groups. Conclusion The data shows geographic differences in distribution of ATC although this preliminary analysis neither explains the nature of these differences nor allows for a clearer view. The rarity of the disease complicates data analysis. This study was also limited by number of cases retrievable from the database itself and lack of granularity in coding available for ATC to find cases of interest, highlighting the difficulty of accurate tumor classifications in large data lakes. Further research into geographical distribution and environmental factors (radioactivity, pollution) of thyroid cancer using more advanced tools, such as GeoSpark, are planned.