We speculate that since serum Cyfra 21.1 is elevated mainly in 131I-refractory thyroid cancer patients or BRAF-mutation-positive patients, using serum Cyfra 21.1 as a diagnostic test of distant metastasis in 131I-avid thyroid cancer patients or BRAF-mutation-negative patients might lower the accuracy. The gene discussed is BRAF; the disease is thyroid gland carcinoma.