Scientists unravel genetic causes of prostate, breast and ovarian cancer

In document NEW SPEC UNIT 1 (TOPIC 2) (Page 118-120)

Ian Sample, science correspondent

The Guardian Wednesday 27 March 2013 17.19 GMT

Research involving 1,000 scientists finds scores of genetic markers that identify people most likely to develop diseases

A prostate cancer cell. More than 40,000 men a year are diagnosed with prostate cancer in Britain and nearly 11,000 die from the disease. Photograph: Steve Gschmeissner/Getty.

A national screening programme for prostate cancer could be introduced by the NHS following an international effort by more than 1,000 scientists to unravel the genetic causes of prostate, breast and ovarian cancer.

The study, the largest to look for the faulty DNA that drives the cancers, revealed scores of genetic markers that can identify people most likely to develop the diseases.

Doctors said a simple £5 saliva test based on the markers could give patients a personalised ‘risk profile’ for the diseases and pave the way for individually tailored screening, with those most at risk having more regular health checks.

A screening service could be offered within five years and would transform treatment for the most common cancer among British men. More than 40,000 men a year are diagnosed with prostate cancer in the UK and nearly 11,000 die from the disease. If the disease is picked up early, the chance of survival is 95%, but that falls to 60% if the disease is spotted later.

Britain has never introduced a national prostate screening programme as existing tests are not precise enough. For every life saved by screening based on the common PSA blood test, 12 to 48 men would be treated unnecessarily for a disease that would never cause them problems.

“Genetic profiling will be able to refine the risks in the population so that we can target screening to those at higher risk,” Eeles said. “We hope that, within five years, we will be able to use this type of technology in the NHS to target screening to those who are most likely to benefit.”

Genetic markers are like spelling mistakes in a person’s DNA that raise the risk of disease. To find markers for prostate cancer, scientists compared the genetic makeup of 25,000 prostate cancer patients with a similar number of healthy men. They found 23 new faults in DNA that increase the risk of developing prostate cancer. Importantly, 16 of these drive the most aggressive and life-threatening forms of the disease.

While most men carry a small number of the genetic markers for prostate cancer, the 1% with the most genetic faults face nearly a five-fold increased risk of the disease. These men have a one in two chance of developing the disease.

Alan Ashworth, chief executive of the Institute of Cancer Research, said the research “changes the game” for applying genetics to the management of prostate cancer. “Screening for different levels of risk becomes a real possibility,” he said.

A similar investigation into breast cancer found 49 new genetic faults that appear to drive the disease. Women who inherit most of these have a 30% chance of developing the disease, more than three times the national average. Some of the faults were only predictive of the most aggressive, and dangerous, form of the cancer, called oestrogen receptor negative breast cancer.

Women who carry mutations in genes called BRCA are already known to have a substantially higher risk of breast cancer, at around 65%. But the latest study shows that women who have a BRCA mutation, and carry many of the newly-discovered gene defects, are 80% more likely to develop the disease.

In the third part of the project, which involved 130 institutions from around the world, scientists compared the genetic makeup of ovarian cancer patients with healthy women. The study found eight new gene regions that raise the risk of the disease, bringing the known total to 12. Together, these had a marginal effect on cancer risk, raising the chance of disease from 1.8% to 4%.

Eeles said a simple test at a GP surgery could be read by a computer to give each patient a personalised risk profile for the disease. Once the tests are available, doctors could improve their accuracy by adding lifestyle factors into the risk assessment. For example, the risk of breast cancer is raised by alcohol and a high-fat diet, but lowered by childbearing and breastfeeding.

Trials are taking place to work out the best way to use the tests and how any screening programmes might work or be modified where screening already exists.

In the case of prostate cancer, it is not clear at what age men should be tested to determine their risk of the disease. Since prostate cancer usually only develops after the age of 40, an earlier test might cause unnecessary and prolonged anxiety. It is not clear whether men who are found to be at high risk should have blood tests or MRI scans and when doctors should take biopsies.

Salters-Nuffield Advanced Biology Resources

Activity 2.19 Student Sheet

Tests for breast cancer risk pose similar problems, though screening procedures, such as

mammograms, and interventions, from early use of preventative drugs to a precautionary operation to remove the breasts, are more established.

The work, led by the Institute of Cancer Research and Cambridge University, was funded by Cancer Research UK and the Wellcome Trust and published as a series of papers in Nature Genetics and several other science journals.

While the studies transform what is known about the genetics underpinning the three cancers, in each case they account for only 40% of the gene faults that must be involved. To discover the rest, which could be many thousands, scientists will need even larger studies that would involve sequencing a person’s entire genetic makeup.

"Hundreds if not thousands of genes are likely to play a role in how cancers start. But by

understanding why some people seem to be at a greater risk, we can look towards an era where we can identify them and take steps to reduce their chances of getting cancer, or pick up the disease in its earliest stages," said Harpal Kumar, chief executive of Cancer Research UK.

Q1 Compose a letter to The Guardian either supporting or opposing the establishment of national genetic screening programmes for prostate, breast and ovarian cancer. Your letter should concentrate on the social and ethical issues raised in the article and be no longer than 500 words. When presenting your ideas on the ethical issues you can refer to the ethical frameworks presented in the Student Book.

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In document NEW SPEC UNIT 1 (TOPIC 2) (Page 118-120)