Liquid gold

Seventy years ago, a research paper published in France went almost unnoticed, but its findings led to a £250 billion global market in cancer testing. Dermot Martin brings us up to date with liquid biopsies   

Five years before James Watson and Francis Crick cracked the molecular structure of DNA, a research paper on analysis of blood serum was published in post-war Paris.

It described the detection of traces of DNA, known as cell free nucleic acids, in blood serum of patients with cancer. Little appreciated at the time, that 1948 paper by Mandel and Metais heralded the arrival of the process of liquid biopsy and later ignited a global market estimated at north of £250 billion.

In the seventies David Shapiro and others reported finding significantly higher levels of free DNA in patients with certain types of cancer, concluding that serum DNA could be pivotal in identifying and tracking tumour types.1

Seventy years on from the Paris paper, the taking of blood and other body fluids for biopsy is commonplace in cancer research.

These are not like standard blood or urine tests. Liquid biopsies seek clues from trace DNA or circulating cancer cells to the nature of a tumour and hope for new drugs and therapies.

Blood is the usual fluid of choice for liquid biopsy, but urine, saliva and even cerebrospinal fluid are used in some cases. A liquid biopsy’s “selling point” is that it obviates the need for invasive, often painful and risky tissue sampling.

Tissue biopsy limitations

Standard procedure for a liquid biopsy is the extraction of five millilitres of a patient’s blood. The sample is spun down in a laboratory to give two millilitres of plasma, which can be tested for tell-tale free DNA or circulating cancer cells.

As Dr Minetta Liu, an oncologist at the Mayo Clinic in the US, tells the clinic’s own webcast: “What is in the blood is what is biologically relevant in understanding tumours. That is what we should be sampling.”

Traditional tissue biopsies have limitations. A tumour changes over time as it grows, spreads and is exposed to anti-cancer medications. That means tissue biopsies, taken when the disease is first diagnosed, may not reflect the current state.

Liquid biopsies can be used not only for diagnosis but for serial measurement of a tumour, making for smarter, better informed clinical decision-making throughout treatment.

Dr Liu says: “Repeating biopsies to get updated information about cancer is invasive and associated with potential complications, including pain, infection and bleeding.”

“Cancer cells that spread to different areas of the body may differ somewhat from the cancer at the site where it started. As a result, a tumour biopsy from one part of the body is unlikely to adequately represent cancer throughout the body.”

The rapid development of gene-sequencing machines that can rapidly decode millions of short fragments of DNA now generates vital information related to tumours. The results are compared with the reference map of the human genome and clinicians hope to identify the specific patterns of rearranged DNA and untangle the story of the tumour.

As a result there is a global technology race to develop tests for all forms of cancer. The longer-term goal is for a world in which medicine is personalised.

Angle’s Parsortix

One company, Surrey-based ANGLE PLC, has spent years developing cell separation techniques from liquid biopsies.

ANGLE’s CEO Andrew Newland believes the company has perfected a system that could be the touchstone for techniques to help accurately diagnose and map cancers of all types.

“At the outset, we were looking for ways of separating foetal blood from a mother’s blood in order to help the study of pre-natal diseases and genetic conditions,” says Newland. “Over the years, we have fine-tuned our technology and evolved our system to the point where we can separate minute populations of cancer cells from normal blood cells.

“Tumour cells in blood have enormous value for researchers, perhaps greater than trapping and mapping trace DNA. However, they are notoriously difficult to isolate. Trace DNA is helpful for tracking cancers but living cancer cells can be cultured, analysed and monitored to greater effect.”

ANGLE’s Parsortix is a system that can trap those illusive cancer cells.

Newland says: “Parsortix is at the forefront as a separation technique capable of capturing circulating tumour cells (CTCs) at concentrations as low as one CTC per billion healthy cells.

CTCs are the mechanism by which cancer spreads through the body. Improving their detection and analysis has huge implications for cancer research, diagnosis and treatment.

Mr Newland said: “We have made huge strides with this technique. Samples from liquid biopsy applied to the Parsortix method are providing analytical data across the entire range of cancers and helping to track the progress of the disease in individual patients.”

Precision medicine

Liquid biopsies have opened up the route to precision medicine especially in cancer therapy. An individual disease type can be identified which opens the door to drugs specific to an individual. It is already changing the way we develop new drugs. So much effort is invested developing treatments which have too broad an application and the resulting treatment might not be suitable for one person but work well in another situation.

They can inform treatment decisions in lung cancer with an epidermal growth factor receptor (EGFR) mutation. The method can be used to track the progress of cancer patients, checking whether a tumour has responded to treatment or has developed new mutations. If so, that might prompt a change in treatment plan.

Liquid biopsies can be used not only for diagnosis but for serial measurement of a tumour, making for smarter, better informed clinical decision-making throughout treatment. They can help create specific tests for cancer types.

Joakim Jagorstrand, Lifecycle Leader for Genomics and Oncology at Roche Diagnostics, says liquid biopsy will never replace the tissue biopsy in the foreseeable future.

“They are complementary to the tissue biopsy allowing more patients to be tested. It is a minimally invasive technique which for example might change the prognostic and predictive landscape for lung cancer genotyping and impact patient management.”

Liquid biopsies can help detect epidermal growth factor receptor (EGFR) gene mutations, which occur in 10-35% of patients with non-small cell lung cancer (NSCLC). It will help doctors to choose the right treatment for the right patient at the right time.

Companion diagnostics

There is the potential of diagnosis focused on the individual patient. Is the optimism over this approach misplaced? Not at all, say the advocates who believe it can identify patients who are most likely to benefit from a particular therapeutic product.

Patients at higher risk of serious side effects as a result of treatment with a specific therapeutic product can be more easily identified. It should make it easier to monitor treatment and adjust it to achieve improved safety or effectiveness.

Researchers are using so-called companion diagnostics, a test applied in advance of the therapeutic drug to determine its suitability for a specific patient. CDs are developed based on companion biomarkers which help predict a likely response to, for example, severe toxicity. They could revolutionise drug development and have the potential to personalise treatment. The biomarkers depend on the information gained from liquid biopsy.

A good example is Her2?gene in breast cancer and availability of companion drugs. Over 15 years clinicians have changed the standard of care, and outlook, for those affected.?In approximately 20% of breast cancers?the Her2 is over expressed so the protein appears at high levels. This also happens in some stomach?cancers and other malignancies.

The knowledge that a breast tumour is either Her2 positive, or negative, can make all the difference in a breast cancer patient's course, especially in terms of survival – which is why companion diagnostics and their accuracy are so inviting.

Precision medicine demands patient stratification, which basically means identifying target patients who are more likely to benefit from therapy.

So personalised companion diagnostics should reduce drug development time and costs, and may result in cheaper drugs and greater effectiveness. This new approach is all dependent on technology linked to liquid biopsies.

Dr Minetta Liu says: “What is in the blood is actually what is relevant. One could argue it is not the overall tumour composition that we really want. We want the biologically relevant population. How do we define that?  If that’s in the blood, that’s what we should be sampling. It’s that global representation of tumour biology that we need to understand.”

Reference

1. Leon, S.A.; David Shapiro, B.; Sklaroff, D.M.; Yaros, M.J. Free DNA in the serum of cancer patients and the effect of therapy.?Cancer Res.?1977,?37, 646–650. 

Author:

Dermot Martin is a freelance science writer