Effect of <i>BRAF^V600E</i> on response to sorafenib in advanced thyroid cancer patients

Abstract

6002 Background: We are conducting an open-label phase II study of sorafenib in patients with metastatic, iodine-refractory thyroid carcinoma. Methods: 55 Patients were administered sorafenib 400 mg orally BID. Responses were monitored by PET and CT. Primary endpoints were response rate (RR) and progression free survival (PFS) by RECIST criteria. BRAF and RAS mutation status is determined by DNA sequencing. Outcome data is evaluated using the Kaplan-Meier method and log-rank test. Biologic activity in tissue obtained during treatment at response and progression is being explored using immunohistochemistry (IHC) to pERK, pAKT and Ki-67 among others, in pretreatment blocks from virtually all patients, and a subset of 14 patients in whom on-treatment tissue is available. Results: We have completed accrual of the 55 patients planned for enrollment; median time on study is 34 weeks and 25 pts (45%) are male. Histological subtypes include papillary (PTC): 25 pts (47%); follicular/Hürthle Cell (FTC): 19 pts (36%); medullary: 4 pts (8%), and poorly differentiated/anaplastic: 5 pts (9%). 52/55 patients are evaluable for response at this time. Median PFS was 84 wks. Genotyping of BRAF is complete in 16 patients. For patients with PTC/FTC, the PFS for those with BRAF wt was 54 wks compared to 84+ wks for patients with BRAF V600E (p = 0.028). On-treatment tissue at progression demonstrates heterogeneity, with p-ERK and p-AKT suppressed in some areas, but highly expressed in others. Data at 6 months post accrual of the last patient will be presented along with patient thyroglobulin levels, PET and CT scans. IHC and additional genotyping will also be presented. Conclusions: Sorafenib has activity in patients with advanced thyroid cancer with an overall PFS of 84 wks. While most patients with PTC or FTC achieve durable responses, patients whose tumors harbor BRAF V600E have significantly longer PFS than those that are BRAF wt . [Table: see text]