BACKGROUND: Anaplastic thyroid carcinoma (ATC), a rare and highly malignant 
tumor, has long been thought to arise from well-differentiated carcinoma (WDC) 
such as follicular thyroid carcinoma (FTC) and papillary thyroid carcinoma 
(PTC). The purpose of this study was to test this notion by examining whether 
and, if so, how often ATC harbors the oncogenes that are commonly associated 
with WDC, such as RAS in FTC and BRAF in PTC.
METHODS: We analyzed the mutation hotspots of BRAF (codon 600) and N-, K-, and 
H-RAS (codons 12, 13, and 61) in 16 ATCs. We also examined two genes, PIK3CA 
(exons 9 and 20) and TP53 (exons 5-9), both of which have been reported in ATCs.
RESULTS: The results showed that approximately 31% (5 of 16) of ATCs harbored 
N-RAS mutation, 6% (1 of 16) had mutated BRAF, and approximately 56% (9 of 16) 
had mutated TP53. As to the three ATCs that had coexisted PTCs, mutated BRAF was 
detected in all PTC components but only in one ATC, while mutated PIK3CA was 
found in only one PTC component but not in the ATC.
CONCLUSION: A number of ATCs arise from WDCs, more often from RAS-mutant tumors 
than from BRAF-mutant tumors, implying that particular attention should be paid 
to the WDC harboring RAS mutation.