A tumor sample shows an allele frequency of 5% for a specific KRAS mutation. Which sequencing artifact is most critical to rule out before reporting this finding?
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Correct answer: FFPE-induced cytosine deamination artifact
FFPE preservation often causes cytosine deamination, converting cytosine to uracil, which is read as thymine during PCR. This results in C>T/G>A artifactual mutations at low allele frequencies. Confirmation via a non-FFPE sample or using uracil-DNA glycosylase (UDG) treatment is recommended.
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