The Rise of ctDNA, Part One
New ctDNA assays could make more metastatic melanoma cases detectable
Roisin McGuigan |
A new blood plasma test that detects circulating tumor DNA (ctDNA) could help identify mutations in metastatic melanoma that are tough to spot using current methods, according to researchers at NYU Langone Medical Center, USA (1).
BRAF and NRAS mutations account for over half of the 50,000 melanoma cases diagnosed in the US – but what about the rest? Though telomerase reverse transcriptase (TERT) promotor sequence mutations appear in up to 85 percent of all metastatic melanomas (2), the high G-C content of the TERT sequence can make such mutations difficult to detect using more traditional sequencing technology. The problem – and potential – prompted David Polsky, senior investigator of the associated study, to try an alternative technology – mutation-specific droplet digital PCR – and successfully developed a pair of tests that can detect changes in two mutation hot spots in the sequence. The assays were able to detect TERT mutations with high sensitivity and specificity; in tumor and plasma samples from patients with and without metastatic melanoma, all cases were detected successfully, with no false positives – even with as little as 1 percent of the mutated ctDNA present in a 5 ml blood plasma sample.
The blood tests could offer an alternative to CT scans – and the resulting radiation exposure – and allow more convenient and frequent testing that covers a wider range of melanomas, explained Polsky (3). He is hopeful that, once validated, the tests will quickly see widespread use. “Our goal is to use these tests to make more informed treatment decisions and, specifically, to identify as early as possible when a treatment has stopped working, cancer growth has resumed, and the patient needs to switch therapy,” he added.
- B Corless et al., “Detection of TERT C228T and C250T promoter mutations in melanoma tumor and plasma samples using novel mutation-specific droplet digital PCR assays”, Paper presented at the American Associate for Cancer Research 2017 Annual Meeting, April 1–5, Washington, DC, USA. Session PO.CL01.01 – 743 / 9.
- S Horn et al., “TERT promoter mutations in familial and sporadic melanoma”, Science, 339, 959–961. PMID: 23348503.
- EurekAlert!, “New gene-based blood tests identify more skin cancers”, (2017). Available at: bit.ly/2qjrUfb. Accessed May 15, 2017.