OBJECTIVE: Anaplastic thyroid carcinoma (ATC) is a rare and aggressive thyroid neoplasm. This study is the largest to date and aims to provide the most up-to-date analysis of demographics and clinicopathological factors of ATC. METHODS: Data for this study were extracted from the Surveillance, Epidemiology, and End Results (SEER) database. RESULTS: A total of 1,769 cases of ATC were included with a median age at diagnosis was 71 years, and 59% were females. The most common site of metastasis was the lung (40.7%). The majority of patients underwent combination therapy (surgery with adjuvant chemoradiation) (19.2%). The 5-year OS was 7.3% (95% C.I. 6.6-8.0). The 5-year CSS was 11.8% (95% C.I. 10.8-12.8). The highest 5-year survival was observed with combination therapy (surgery with adjuvant chemoradiation) at 20.9%. Multivariable analysis revealed that age >
60 years, Asian/Pacific Islander, >
2 cm tumor size, and metastatic disease were independent risk factors. CONCLUSIONS: ATC is an uncommon tumor that mainly affects Caucasian females in their 70s. Older age, Asian/Pacific Islander race, and larger tumor size (>
2 cm) were also associated with a worse prognosis. For better comprehension of pathogenesis, prospective clinical trials should include patients from all ethnicities, gender, and genomic analysis of ATC.