Doctors welcome blood test that predicts whether breast cancer will return years before it shows up on scans

A blood test can predict whether breast cancer will return years before it shows up on scans, allowing treatment to begin before it becomes incurable.

The “ultra-sensitive” test can detect traces of DNA from a tumor before a full relapse, when it is much more difficult to treat.

It was found to be 100% accurate in predicting which patients would see their cancer return – up to three and a half years before conventional scans.

Doctors say it could have a “transformative effect” on breast cancer outcomes, saving many of the 11,500 lives lost each year in the UK to the disease.

“Liquid biopsy” uses whole genome sequencing to look for genetic defects in a patient’s DNA, which may be a sign of cancer.

Researchers from the Institute of Cancer Research (ICR) in London carried out the trial on 74 women with different types of early breast cancer.

The test looks for 1,800 mutations in the blood that are released by cancer cells – known as circulating tumor DNA (ctDNA).

He managed to spot this ctDNA in 11 women – all of whom saw their cancer return. None of the other women relapsed.

Blood samples were analyzed at diagnosis and again after surgery and chemotherapy. The tests were then repeated every three months for the following year and every six months for five years.

On average, the blood test detected cancer 15 months before symptoms appeared or showed up on scans – the method currently used by the NHS to monitor cancer survivors.

The earliest was 41 months before a CT scan confirmed the diagnosis, according to findings presented at the American Society of Clinical Oncology conference in Chicago.

All those who had evidence of tumor DNA at any time after surgery had a higher risk of future relapse and poorer overall survival.

Lead researcher Dr Isaac Garcia-Murillas of the ICR said the findings “lay the foundation for better post-treatment follow-up and potentially life-extending treatment for patients”.

He added: “Breast cancer cells may remain in the body after surgery and other treatments, but there may be so few of these cells that they are undetectable in follow-up exams. These cells can cause patients to relapse several years after their initial treatment.

“Ultrasensitive blood tests could offer a better approach for long-term monitoring of patients whose cancer is at high risk of recurrence.”

Other blood tests have also been developed to look for DNA evidence of recurrent cancer. However, these only look for 16 to 50 mutations in gene regions directly linked to the disease.

Developed by the American company Personalis, this new test is approximately 100 times more sensitive.

Dr Garcia-Murillas added: “A more sensitive test is very important for this group of patients with early breast cancer, because they tend to have a very low amount of cancer DNA in their blood.”

Women who relapsed in the study survived an average of just over five years.

Researchers said further studies were underway to see if patients could begin treatment as soon as signs of recurrence were detected, preventing the disease from spreading and becoming incurable.