High prevalence and possible de novo formation of BRAF mutation in metastasized papillary thyroid cancer in lymph nodes

Context: The role of the T1799A BRAF mutation in lymph node metastasis of papillary thyroid cancer (PTC) is not clear. Objective: Our objective was to explore the relationship between BRAF mutation and lymph node metastasis of PTC by examining the mutation in both the primary tumors and their paired lymph node metastases. Design: We isolated genomic DNA from primary thyroid tumors and paired lymph node metastases and performed direct sequencing of exon 15 of the BRAF gene mutation that carries the T1799A mutation. Results: In a series of 33 cases, 21 harbored the T1799A mutation in the primary tumors, and 17 (81%) of them harbored the same mutation also in the paired lymph node metastases. Twelve cases did not harbor the T1799A mutation in the primary tumors, among which nine cases also did not harbor BRAF mutation in the lymph node-metastasized tumors, whereas the other three did harbor the T1799A mutation in lymph node-metastasized tumor tissues. A novel tandem TG1799-1800AA mutation within one allele was found in a lymph node-metastasized tumor but not in the primary tumor. This mutation results in the change of codon 600 (GTG) of the gene to GAA with the consequent amino acid change (V600E) in the B-type Raf (BRAF) protein, same as that caused by the T1799A mutation alone. Conclusion: The high prevalence of BRAF mutation in lymph node-metastasized PTC tissues from BRAF mutation-positive primary tumors and the possible de novo formation of BRAF mutation in lymph node-metastasized PTC were consistent with a role of BRAF mutation in facilitating the metastasis and progression of PTC in lymph nodes.