• Background: BRAFV600E is the most frequent oncogene in differentiated thyroid cancer (DTC) occurring in about 50% of cases. Clinical trials with tyrosine kinase inhibitors (TKI) with specific activity against BRAF in metastatic radioiodine-resistant DTC (MRR-DTC) are ongoing. Very recently it has been demonstrated that DTC often consists of a mixture of tumor cells with wild-type and mutant BRAF. The subclonal occurrence of BRAFV600E in MRR-DTC could disable the therapy with BRAF targeted TKI and be responsible of the frequent defeats of this treatment. A therapeutic strategy based upon BRAF inhibitors in tumors bearing subclonal BRAFV600E could be initially successful hitting the tumor cells expressing the oncogene, and after the initial tumor growth arrest and/or shrinkage, the oncogene negative cells insensitive or less sensitive to the treatment, could restart the growth of the tumor causing the progression of the disease and the escape from the clinical response.
• Aims: To determine the impact of subclonal BRAFV600E on the efficacy of BRAF inhibitors in the treatment of MRR-DTC.
• Study design: Primary tumor tissues will be analyzed for the presence of BRAFV600E by pyrosequencing or other quantitative assay. If available, synchronous metastases and post-therapy metachronous metastases will be analyzed as well. The clinical response will be determined according to RECIST, and the association with the percentage of BRAFV600E alleles will be evaluated. Attention will be paid to the possible difference of BRAFwild-type/BRAFV600E ratio between primary tumors and synchronous metastases, primary tumors and post-therapy metachronous metastases, and between responsive and resistant synchronous tumor lesions.

Inclusion Criteria:

• subjects any sex any age with metastatic or unresectable thyroid carcinoma treated with tyrosine kinase inhibitors
• evidence of measurable disease by Response Evaluation Criteria in Solid Tumors (RECIST)
• availability of study end points including best response, duration of response, and time to disease progression (based on RECIST), clinical progression, or death
• availability of tumor tissue samples, frozen or formaldehyde fixed-paraffin embedded from block, genomic DNA already extracted from tumor tissue

Exclusion Criteria:

• concurrent Hashimoto's thyroiditis

primary care clinic