Blood Test Gives Early Warning of Melanoma Relapse

Targeted immunotherapies have transformed melanoma care, extending median survival from around 9 to over 25 months but nevertheless, most patients still die of their disease and although most melanoma patients respond to treatment at first, their cancer can become resistant within a year.

Improved understanding of the genetic landscape of melanoma has facilitated development of effective targeted therapies and improved knowledge of the molecular controls of the immune system has driven the development of immune checkpoint inhibitors. However, not all patients benefit from these treatments and resistance is a persistent problem.

Scientists at the University of Manchester (UK) developed protocols to facilitate individualized treatment decisions for advanced melanoma patients, analyzing 364 samples from 214 patients. Whole exome sequencing (WES) and targeted sequencing of circulating tumor DNA (ctDNA) allowed them to monitor responses to therapy and to identify and then follow mechanisms of resistance.

Blood was collected into tubes, double-centrifuged at 10,000×g for 10 minutes at room temperature and the plasma stored at -80 °C within four hours of collection. Circulating cell-free DNA (cfDNA) was extracted with QIAamp Circulating Nucleic Acid Kits (Qiagen; Valencia, CA, USA), and quantified by TaqMan RNAseP Assay (Life Technologies; Carlsbad, CA, USA) and stored at -80 °C. Multiplexed with sequencing libraries of higher complexity to facilitate clustering were processed on a MiSeq (Illumina; CA, USA). Real-time polymerase chain reactions were processed on an ABI 7900HT Real-time PCR machine (Applied Biosystems; Foster City, CA, USA).

Whole exome sequencing (WES) of tumors revealed potential hypothesis driven therapeutic strategies for B-Raf proto-oncogene, serine/threonine kinase (BRAF) wild-type and inhibitor-resistant BRAF mutant tumors, which were then validated in patient-derived xenografts (PDXs). The investigators also developed circulating tumor cell-derived xenografts (CDX) as an alternative to PDXs when tumors were inaccessible or difficult to biopsy.

Richard Marais, PhD, a professor and lead author of the study, said, “Being able to spot the first signs of relapse, so we can rapidly decide the best treatment strategy, is an important area for science. Using our technique, we hope that one day we will be able to spot when a patient's disease is coming back at the earliest point and start treatment against this much sooner, hopefully giving patients more time with their loved ones. Our work has identified a way for us to do this but we still need to test the approach in further clinical trials before it reaches patients in the clinic.” The study was first published online on December 29, 2015, in the journal Cancer Discovery.

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