The role of BRAF V600E mutation in post-surgical 131I therapy in papillary thyroid carcinoma. A study based on SPECT-CT uptake analysis.

BACKGROUND The BRAF V600E mutation (BRAF mut) in papillary thyroid cancer (PTC) has been associated with poor response to therapy with 131I in patients with metastases but the results in postsurgical treatment are controversial. Our main objective is to investigate the impact of the mutation on the biokinetics of the administered 131I therapy after surgery. MATERIALS AND METHODS A prospective study was designed, from July 2015 to January 2018 which included patients with PTC receiving 131I therapy after surgical treatment. To study the biokinetics of the radioiodine in postoperative thyroid remnants, SPECT-CT images were acquired so as to obtain the following variables: percentage of remnant uptake at 2d and 7d postadministration, effective half-life and time-integrated activity coefficient. All of them were compared depending on the mutational diagnosis and other clinical features and pathological variables. RESULTS Sixty-one patients, and in total 103 thyroid remnants, were included. 59% of patients were BRAF mutated. The mutation was associated with classic variant (88.5% vs 11.5%; p=0.0001), desmoplastic reaction (85.7% vs 14.3%; p=0.002), smaller tumour size (1.5cm vs 2.1cm; p=0.024), nodal disease (3.3 vs 1; p=0.001) and advanced stages (76.9% vs 23%; p=0.014). The BRAFmut group had a lower percentage of 131I uptake at 2d (0.17% vs 0.47%; p= 0.001) and at 7d (0.02% vs 0.1%; p=0.013); and a lower timeintegrated activity coefficient (0.05h vs 0.17h; p=0.002). In univariate analysis, in addition to the mutation, the histological variant was significant but only for timeintegrated activity coefficient (p=0.04). In multivariate analysis, only mutation determined the 2d uptake (p<0.001) and the time-integrated activity coefficient (p<0.001). CONCLUSIONS The BRAF V600E mutation is associated with lower 131I uptake in thyroid remnants. Furthermore, it is an independent factor that decreases the effect of post-surgical 131I therapy, and therefore, it could be used as a potential tool to optimize the treatment of PTC.