Comparative evaluation of the new FDA approved THxID™-BRAF test with High Resolution Melting and Sanger sequencing

Since patients diagnosed with BRAF V600E and V600K mutated advanced melanoma show response to treatment with MAP kinase inhibitors, several sensitive methods have been developed to determine the V600 allele status of melanoma patients. Vemurafenib (Zelboraf) and dabrafenib (Tafinlar) are specific BRAF V600 inhibitors recently approved by the US FDA as single agent treatments for unresectable or metastatic melanoma in patients with the BRAF V600 mutation.

We assessed the new CE THxID™-BRAF diagnostic test, which is also FDA-approved as a companion diagnostic test in the US under a specific reference and compared the results of this assay with both High Resolution Melting (HRM) and Sanger sequencing in 113 melanoma FFPE samples.

Invalid results were observed in 0/113 specimen with HRM, 5/113 (4.4%) with Sanger sequencing, and 1/113 (0.9%) with the THxID™-BRAF test. Positive percentage agreement (PPA) was 93.5% (95% CI 82.5 - 97.8) for V600E and V600K mutations combined for the THxID™-BRAF test and HRM, and negative percentage agreement (NPA) was 100.0% (95% CI 94.5 - 100.0). For the THxID™-BRAF test and Sanger, PPA was 100.0% (95% CI 92.1 - 100.0) and NPA 100.0% (95% CI 94.2 - 100.0). One V600E sample identified by THxID™-BRAF test was detected as wild-type by HRM and uninterpretable by Sanger. All V600K (n = 3) were detected using the 3 different approaches. Finally, percent agreement values were not significantly different when using punches (n = 77) vs. slides (n = 36) or depending on samples characteristics such as pigmentation, necrosis, and tumor content.

This study demonstrated the high agreement between the FDA approved THxID™-BRAF assay, HRM, and Sanger sequencing. It has also highlighted the potential of THxID™-BRAF to be applied to a broader range of sample types than claimed in the current "instructions for use", an extension that would require the ad hoc validation and approval.