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DNA-based blood tests to detect skin cancers

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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.

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