B191
A rapid and sensitive assay to detect RET M918T mutations in tumor samples from patients with sporadic medullary thyroid cancer
James Sherwood, Gillian Ellison, John C Smith, Alan Wookey, Anderson Ryan
AstraZeneca, Alderley Park, UK
Vandetanib is a once-daily, orally available anticancer drug with potential for broad and potent antitumour activity by selectively targeting VEGF-dependent tumour angiogenesis and EGFR- and RET-dependent tumour cell proliferation. Phase III evaluation of vandetanib in advanced non-small-cell lung cancer and medullary thyroid cancer (MTC) is ongoing. The constitutively active RET proto-oncogene is a key factor in the development of both inherited and sporadic forms of thyroid cancer. RET M918T is the most commonly observed mutation in sporadic MTC, being found in approximately 40% of patients. We have developed an assay to detect the RET M918T mutation in patients with sporadic MTC. Here, we describe an Amplification Refractory Mutation System (ARMS) assay coupled with a fluorescent detection probe in a real-time format that specifically and sensitively detects the RET M918T mutation. The assay was evaluated using a panel of sporadic MTC samples and sensitivity assessed on admixtures of different amounts of mutant and normal DNA. Our assay was able to detect five copies of mutant DNA in a background of 500 copies of normal DNA. Of 23 medullary thyroid tumour samples analysed, 17 were evaluable by the RET M918T ARMS assay and 29.4% of these tumour samples were confirmed as positive for the M918T mutation. DNA sequence at codon 918 was 100% concordant with the results for the RET ARMS assay. In conclusion, the ARMS assay is a rapid and sensitive procedure for detecting RET M918T in tumour samples, and may help to better understand the clinical efficacy of vandetanib in patients with MTC.
