Genetic Testing for Cancer Prognosis

Last month’s news article was about genetic testing to detect increased risk of developing cancer. This month we will look at three advances in genetic testing in patients who already have cancer diagnosed.

A test that uses the latest next-generation DNA sequencing technology to detect mutations across 46 genes that may be driving cancer growth in patients with solid tumours has been developed and will be introduced in the UK National Health Service (NHS). The presence of a mutation in these genes can potentially determine which treatment a patient should receive. The test is being carried out by the BRC Molecular Diagnostics Centre based at Oxford University Hospitals. The new test could save in drug costs by getting patients on to the right treatments straightaway, reducing harm from side effects as well as the time lost before arriving at an effective treatment.

Cancer is often described as a genetic disease, since the transition a cell goes through in becoming cancerous tends to be driven by changes to the cell's DNA. And increasingly, new cancer drugs depend on knowing whether a mutation in a single gene is present in a patient's cancer cells. For example, a lung cancer patient may have a biopsy taken to check for changes in the EGFR gene. If there is a mutation, the patient may then be treated with a drug that works as an EGFR inhibitor. If there is no mutation, such drugs won't work and the patient would get a different drug that would be more effective for them. Knowing the presence or absence of mutations in a certain gene can determine the treatment path for that patient.

A second study recently reported in the New England Journal of Medicine looked at women with advanced breast cancer. Currently these women are monitored for disease progression and what is called the “tumour burden” or amount of cancerous tissue still present in the body by measuring a tumour marker called CA-15.3 or detecting circulating tumour cells in the blood.

The researchers based at the Cancer Research UK Cambridge Institute used new DNA sequencing techniques to measure the amount of small fragments of DNA shed by dying tumour cells. They found that the amount of this specific tumour DNA in the blood was the best measure of tumour burden in the patients. The test needs further study but it has the potential to get a rapid indication as to whether the current cancer treatment is working well or whether it need to be supplemented or changed.

The third study looked at men with prostate cancer. Researchers in Britain and the United States found that by reading the patterns of genes switched on and off in blood cells, they could accurately detect which prostate cancer patients had the worst survival rates. Many prostate cancers are slow-growing and may not spread during the patient’s life span and thus not need treatment. However at present the only way to determine how aggressive a prostate cancer is likely to be through a pathologist looking at biopsy specimens under a microscope. Even this technique is not perfect as the biopsies may not be representative of all the cancer tissue present in the prostate.

Researchers from the UK group looked at nine genes while the US researchers looked at six genes. Both groups found that by separating their patients into groups according to their gene activity they could identify patients with a much shorter life expectancy. In the future measurement of the activity of a limited number of genes may allow doctors to give patients specific treatment appropriate to the type of cancer they have.

Sources & further reading:

Science Daily  (genetic screening to determine cancer treatment)

Medical News Today  (measurement of tumour DNA fragments)

Science Daily  (markers for aggressive prostate cancer)

Reuters  (markers for aggressive prostate cancer)

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