How a cancer survivor developed a blood test that can change cancer care

For many patients treated for breast cancer, follow-up is marked by uncertainty. A mammogram may look normal and there may not be any alarming symptoms – and still, somewhere in the body, the disease may have returned.

For decades, that has been one of the difficult realities in breast cancer care. For cancer researcher Lao Saal, the question of earlier detection is personal. As a teenager, he was diagnosed with leukaemia and spent three years in a clinical trial at the U.S. National Institutes of Health. When he recovered, he could have chosen to leave the experience behind him. Instead, he did the opposite – immersing himself in the subject. 

“I decided to talk to some of my doctors who had treated me and ask them about their research. They invited me to start working in the lab, and that's where I got hooked on the research“, Lao says.

The rest, as they say, is history.

The blood test that sees cancer coming

Later, research brought him to Sweden and Lund University – to an environment where breast cancer has been studied for decades. Here he also found one of the largest population studies of its kind, with data and material from some 23,000 breast cancer patients.
 

For researchers, being able to follow such large patient population is a goldmine, Lao says.

The extensive patient data generated both new insights and new questions. One of those questions stayed with Lao. Could a blood test detect breast cancer relapse before symptoms appear – and earlier than current methods allow?

It turned out to be possible.

The gap in follow-up

At a clinic in Waxahachie, south of Dallas, Texas, breast cancer chief surgeon Valerie Gorman has spent more than two decades following breast cancer patients.

"Historically we haven’t had a great blood test to follow breast cancer. We have lacked reliable blood markers that can tell us whether treatment is working or whether the disease has silently returned elsewhere in the body," Valerie says. 

Instead, follow-up often relied on conversations and imaging. But mammograms cannot detect metastases in other parts of the body, such as the bones. 

"You really haven’t had a great way to find that until somebody’s bones start hurting."

By then, the disease may already have progressed.

The eureka moment

Cancer cells are messy. As they grow, pieces of their DNA can break off and get stitched back together in the wrong order – almost like pages in a book being torn out and rearranged. These unusual DNA patterns, called chromosomal rearrangements, can act like unique fingerprints of a tumour. And since tumours are constantly “shedding” tiny bits of genetic material into our bloodstream, a simple blood sample – also known as “liquid biopsy“ – can be used as a window into what is happening with the tumour.

“Once me and my team had that sort of light-bulb moment, we realised we really should go after these chromosomal rearrangements”, Lao says.

And so the liquid biopsy test, a blood test called Pathlight, became a reality. Studies have shown that it is able to detect extremely small amounts of tumour DNA with very high accuracy and a very low rate of false positive results – identifying signs of relapse a median of 13.7 months earlier than conventional methods. In some patients, signs have been detected as much as three to four years earlier.

Reaching patients for the first time 

The test has been launched in the U.S. for breast cancer and colon cancer. It received Medicaid coverage for breast cancer in May 2025, meaning it will be accessible to more people. Valerie Gorman’s team started using the liquid biopsy in October 2025, and the test has already helped to detect small metastases in women who had no symptoms at all.
 

We wouldn’t even have known to look for it otherwise, Valerie says.
 

The test gives a sense of prognosis – whether the patient is lower-risk or higher-risk – and data shows it can also provide a readout for how patients respond to treatment over time.

Staying one step ahead of cancer

Detecting recurrence earlier allows treatment to begin sooner. And it could eventually help identify which patients truly need more treatment, and which do not. 

“Maybe we’ll learn that some patients don’t need all that chemotherapy,“ Valerie adds.

For many patients, the repeated testing has become emotionally significant.

“It’s almost a celebration when they get their zero,” she says.