Testing for levels of CA125 in the blood is a useful tool for gauging the likelihood of ovarian cancer and could help detect other types of cancer among patients in primary care, according to research presented at the 2019 NCRI Cancer Conference.

Although the CA125 test is already in use in countries around the world, this is the first large study to look at how well it performs in general practice for testing women who have possible symptoms of ovarian cancer.

Researchers say their results could guide women and their GPs on whether more invasive tests are needed to check for ovarian and other cancers.

They also say that clinical guidelines could now be improved to ensure urgent referrals are made for women most at risk.

The research was led by Dr Garth Funston, a Clinical Research Fellow at the University of Cambridge, UK.

He said: "Less than half of women with ovarian cancer survive for five years following diagnosis. The majority of women are not diagnosed until the disease is advanced, which makes it more difficult to cure. It's important that GPs have effective tools to detect ovarian cancer early and ensure patients are referred appropriately. While CA125 is widely used in general practice in the UK and internationally, prior to this study, it was unclear how effective a test it really was in general practice."

The research included data on 50,780 women who visited GPs in England with possible signs of ovarian cancer, such as persistent bloating or abdominal pain, and were tested for levels of CA125 in their blood between May 2011 and December 2014.

Researchers compared the results of these blood tests with data on which women were diagnosed with ovarian cancer or another form of cancer in the 12 months following their blood test.

They discovered that 10 percent of women who had an abnormally high level of CA125 in their blood were found to have ovarian cancer.

This figure is much higher than previously thought and ten times higher than the estimate given in the UK's 2011 NICE (National Institute for Health and Care Excellence) guidelines on ovarian cancer diagnosis.

In women who had abnormal test results and were aged 50 years or older, 15 percent were found to have ovarian cancer, while in women under 50 with high CA125 levels, only 3 percent were diagnosed with ovarian cancer.

Results also showed that around 17 percent of women 50 years or older with an abnormal result were diagnosed with another form of the disease, such as pancreatic, lung or womb cancer.

The large size of the study meant that researchers were, for the first time, able to look in detail at women with different levels of CA125 in their blood in general practice and give more accurate estimates of cancer risk according to those levels.

The amount of CA125 in the blood is measured in units per millilitre (U/ml) and it can range from one to thousands.

Dr Funston and his colleagues found, for example, that women with a CA125 level of 51 U/ml had a 3 percent probability of ovarian cancer.

Three percent is the level of risk at which NICE recommends urgent cancer referral.

Dr Funston said: "Our work shows that CA125 is a very useful test for detecting ovarian cancer in general practice. Our results can be used by doctors to determine the chance of a woman in general practice having ovarian cancer based on the CA125 level. This could help guide decisions made by GPs and their patients about the need for further investigation or referral."

"Our findings also highlight that women with symptoms who are aged 50 years or more and have abnormally high CA125 levels frequently have other types of cancer. It is really important that GPs are aware of this to ensure these cancers are not missed," added Dr Funston. 

Dr Funston and his team continue their work on early diagnosis of ovarian cancer.

Their study of CA125 blood testing forms part of efforts to create a prediction tool to help GPs spot women who may have the disease as early as possible.

Dr Shibani Nicum, Chair of NCRI's ovarian cancer subgroup and consultant medical oncologist at Oxford University Hospitals, who was not involved in the research said: "Diagnosing more cases of ovarian cancer at an early stage could have a big impact on survival and GPs are an essential part of that process. These findings could help doctors interpret test results and inform their decisions about which tests their patients need next. For instance, an older woman who has abnormal CA125 level should be considered high risk for ovarian cancer. Even if she does not turn out to have ovarian cancer, she might have another form of the disease and either way she will probably need an urgent referral." "These finding can also be used to expand on existing clinical guidelines, both in the UK and other countries, to improve ovarian cancer diagnosis at the national and international level," concluded Dr Nicum. 

Source: National Cancer Research Institute (NCRI)