New York: Scientists have developed two new gene-based blood tests that can quickly and reliably detect previously unidentifiable forms of skin cancer.
Researchers at New York University in the US carried out genetic testing of tumour and blood fluid samples from people with and without one of the most aggressive forms of skin cancer. 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, they said.
The new blood tests, which take only 48 hours, 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. "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," said senior study investigator David Polsky.
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.
Polsky said 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. According to Polsky, 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.
Together, BRAF and NRAS mutations account for over half of the 50,000 cases of melanoma diagnosed each year in the US, and each can be found by existing tests. However, the research team estimates that when the new tests become available for use in clinics, the vast majority of all melanomas will be detectable.
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, researchers said....