Does Molecular Genotype Provide Useful Information in the Management of Radioiodine Refractory Thyroid Cancers?
Whether mutation status should be used to guide therapy is an important issue in many cancers. We correlated mutation profile in radioiodine-refractory (RAIR) metastatic thyroid cancers (TCs) with patient outcome and response to tyrosine kinase inhibitors (TKIs), and discussed the results with other published data. Outcome in 82 consecutive patients with metastatic RAIR thyroid carcinoma prospectively tested for BRAF, RAS and PI3KCA mutations was retrospectively analyzed, including 55 patients treated with multikinase inhibitors. Papillary thyroid carcinomas (PTCs) were the most frequent histological subtype (54.9 %), followed by poorly differentiated thyroid carcinoma [PDTC] (30.5 %) and follicular thyroid carcinoma [FTC](14.6 %). A genetic mutation was identified in 23 patients (28 %) and BRAF was the most frequently mutated gene (23 %). Median progression-free survival (PFS) on first-line TKI treatment was 14.6 months (95% CI 9.9-18.4). BRAF mutation positively influenced median PFS, both in the entire TKI-treated cohort (median PFS 34.7 months versus 11.6 months; hazard ratio [HR] 0.29; 95% CI 0.09-0.98; p = 0.03) and in the TKI-treated PTC cohort (n = 22) [log-rank p = 0.086; HR 2.95; 95 % CI 0.81-10.70). However, in TKI-treated patients, PDTC histologic subtype was the only independent prognostic factor for PFS identified in the multivariate analysis (HR 2.36; 95% CI 1.01-5.54; p = 0.048).
Patients with BRAF-mutant PTC had a significantly longer PFS than BRAF wild-type when treated with TKIs. However, due to the small number of BRAF-mutant patients, further investigations are required, especially to understand the potential positive effect of BRAF mutations in RAIR TC patients while having a negative prognostic impact in RAI-sensitive PTC patients.