Primary Versus Secondary Anaplastic Thyroid Carcinoma: Perspectives from Multi-institutional and Population-Level Data.

Primary (or de novo) anaplastic thyroid carcinoma (ATC) is ATC without pre-existing history of differentiated thyroid carcinoma (DTC) and no co-existing DTC foci at the time of diagnosis. Secondary ATC is diagnosed if the patient had a history of DTC or co-existing DTC components at time of diagnosis. This study aimed to investigate the incidence, clinical presentations, outcomes, and genetic backgrounds of primary versus secondary ATCs. We searched for ATCs in our institutional databases and the Surveillance, Epidemiology, and End Result (SEER) database. We also performed a systematic review and meta-analysis to analyze the genetic alterations of primary and secondary ATCs. From our multi-institutional database, 22 primary and 23 secondary ATCs were retrieved. We also identified 620 and 24 primary and secondary ATCs in the SEER database, respectively. Compared to primary ATCs, secondary ATCs were not statistically different in terms of demographic, clinical manifestations, and patient survival. The only clinical discrepancy between the two groups was a significantly larger tumor diameter of the primary ATCs. The prevalence of TERT promoter, PIK3CA, and TP53 mutations was comparable between the two subtypes. In comparison to primary ATCs, however, BRAF mutations were more prevalent (OR = 4.70; 95% CI = 2.84-7.78) whereas RAS mutations were less frequent (OR = 0.43; 95% CI = 0.21-0.85) in secondary tumors. In summary, our results indicated that de novo and secondary ATCs might share many potential developmental steps, but there are other factors that suggest distinct developmental pathways.