Abstract C24: Detection of BRAFV600E in cell free DNA from patients with papillary thyroid cancer.
Authors: Sherman Eric , Cohen Ezra E.W. , Cabanillas Maria E. , Gianoukakis Andrew , Tai Yu Chuan , Langland Rachel A. , Brose Marcia S. 
Published: August 2014

Detection of mutant DNA from blood has shown increasing usefulness in diagnosis and prognosis for cancer patients. Most studies have focused on lung cancer and colorectal cancer while relatively little is known about the significance of the liquid biopsy in thyroid cancer. Here we describe the outcome of an exploratory study designed to correlate the prevalence of BRAFV600E mutations in tumor and cell free DNA (cfDNA) isolated from serum and plasma collected from papillary thyroid cancer (PTC) patients screened for enrollment in the NCT01286753 study. Further, we examined clinical characteristics that could predict our ability to detect the mutation in cfDNA. NCT01286753 is a phase II efficacy study of the BRAF inhibitor vemurafenib in patients with metastatic or unresectable PTC resistant to radioactive iodine therapy and harboring BRAFV600E. Blood samples were collected at the time of enrollment and DNA was later isolated from 1-2ml of plasma and serum. Mutation detection was performed with a research version of the cobas® BRAF v2 test which has 0.01% or better sensitivity for BRAFV600E. Of 105 patients screened, 69 samples representing 68 unique patients were available for testing. Of these 68, BRAFV600E tissue status was known for 65. We detected the mutation in 26/68 (38%) plasma samples and 29/67 (43%) serum samples. The overall agreement between mutation calls from plasma and serum was 91%. The overall concordance between tissue mutation status and cfDNA mutation status was 55% for plasma and 61% for serum. No mutations were detected from patients with wild type tissue samples. We estimated the total DNA recovered from each sample using Cp values, and looked for correlation to age, stage, or tumor burden. We were unable to attribute statistical significance to any of the variables examined. Performing a logistic regression analysis on the tissue positive sample set and adjusting for potential cofounders, we examined clinical characteristics that could influence our ability to detect the mutation in cfDNA. We found that we were more likely to detect the mutation in plasma if the patient had recently undergone prior oncology therapy (p value &lt; 0.0001, OR = 2.92) or if the patient had a greater tumor burden as measured by the sum of RECIST tumors (p value = 0.011, OR = 1.75) and the sum of target lesion diameter (p = 0.03, OR = 1.07). We were also more likely to detect the mutation in plasma from patients that had histologically unresectable disease (p value = 0.041, OR = 8.93). Efforts to increase sensitivity could include using a higher serum or plasma sample volume. In the future, detection of mutant BRAF from the plasma of PTC patients could serve as an alternative method for mutation detection, especially when tissue is unavailable.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C24.

Citation Format: Eric Sherman, Ezra E.W. Cohen, Maria E. Cabanillas, Andrew Gianoukakis, Yu Chuan Tai, Rachel A. Langland, Marcia S. Brose. Detection of BRAFV600E in cell free DNA from patients with papillary thyroid cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C24.