Researchers have developed two new gene-based blood test that can reliably diagnose previously unidentifiable forms of skin cancer.
These new tools are the first to identify melanoma DNA in the blood of patients whose cancer is spreading and who lack defects in either the BRAF or NRAS genes, already known to drive cancer growth.
Having quick and accurate monitoring tools for all types of metastatic melanoma may make it easier for physicians to detect early signs of cancer recurrence, researchers said.
"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", says senior study investigator and dermatologist David Polsky, MD, PhD.
The new tests monitor blood levels of DNA fragments, known as circulating tumour DNA (ctDNA), that are released into the blood when tumour cells die and break apart.
The test detects evidence of changes in the chemical building blocks (or mutations) of a gene that controls telomerase reverse transcriptase (TERT), a protein that helps cancer cells maintain the physical structure of their chromosomes.
According to Polsky the detected changes occur in mutant building blocks, in which a cytidine molecule in the on-off switch for the TERT gene is replaced by another building block, called thymidine. Either mutation, C228T or C250T, results in the switch being stuck in the “on” position, helping tumour cells to multiply.
He further added that the blood tests may have advantages over current methods for monitoring the disease because the tests avoid the radiation exposure that comes with CT scans, and the tests can be performed more easily and more often.
These tests, once clinically validated, are also likely to gain widespread use quickly.
As part of the ongoing study, researchers checked results from the new tests against 10 tumour samples taken from patients diagnosed with and without metastatic melanoma. They also tested four blood plasma samples (the liquid portion of blood) from patients with and without the disease.
Blood test results matched correctly in all cases known to be either positive or negative for metastatic melanoma.
Successful detection occurred for samples with as little as one per cent of mutated ctDNA in a typical blood plasma sample of 5 millilitres, scientists said.
The new blood tests, which take only 48 hours, were developed in conjunction with Bio-Rad Laboratories in Hercules, Calif and are currently only available for research purposes.