The tumour trail left in blood

from Nature by Kelly Rae Chi –

Liquid biopsies can detect cancer signs from a blood sample, without the need for invasive procedures. But further work is needed before they can become reliable diagnostic tools.

A lung biopsy is an invasive and uncomfortable procedure — especially for an 80-year-old grandmother. But by profiling his elderly patient’s tumours in this way, lung oncologist Geoffrey Oxnard could target them with a matched drug. After treatment, his patient’s tumours seemed to disappear.

Then, some time later, the 80-year-old returned to Oxnard’s clinic riddled with pain. Tests showed that the cancer had returned, and hunting down a genetic cause of this resistance would require another invasive lung biopsy.

But Oxnard, who is at the Dana-Farber Cancer Institute in Boston, Massachusetts, offered the woman an alternative: “Let’s just check your blood.” He performed what’s known as a liquid biopsy, using nothing more than a blood sample. Within a day, he spotted minuscule amounts of tumour DNA that revealed a mutation that causes resistance to treatment. Luckily, a drug that targets the mutation was being tested in clinical trials. With the genetic profile in hand, Oxnard managed to enrol his patient into the study, and her tumours went into remission again.

The discovery that parts of tumour cells, or even whole cells, break away from the original tumour and enter the bloodstream led to the idea of liquid biopsies. With this approach, cancers can be genetically characterized by analysing tumour DNA taken from a blood sample, thus bypassing the need to extract solid tumour tissue. Now, the rise of rapid genome-sequencing techniques has made it practical to translate this concept to the clinic. Three main approaches are being pursued: analysing circulating tumour DNA1, examining whole tumour cells in the bloodstream2 and capturing small vesicles called exosomes that are ejected by tumours3 (see ‘Scalpel-free biopsies’). And scientists have found that blood platelets might be able to offer up cancer clues, too (see ‘Platelets ingest tumour data’).

The allure of liquid biopsies is that they are quick, convenient and minimally painful, and they allow clinicians to closely monitor how tumours respond to therapies and to forecast cancer recurrences. In the long term, clinicians might even be able to use liquid biopsies to catch tumours at the earliest stages, before a person shows any symptoms. The genomic information in DNA circulating in the bloodstream could provide a snapshot of cancer genes in the body and may even point to where the cancer originated.

Investors are excited, and funds are pouring into start-ups focused on liquid biopsies. Sequencing firm Illumina of San Diego, California, for example, launched a spin-off company in January called Grail that will develop a plasma-based genetic screen for the early detection of multiple cancers.

But extensive testing is required before liquid biopsies can supersede surgical biopsies in the clinic. And there are still concerns from regulators about the sensitivity and accuracy of these procedures — for example, Oxnard’s patient was required to have another, conventional biopsy to confirm the results of the liquid biopsy before she was allowed to enrol in the clinical trial.

Nevertheless, researchers say that it is no longer a question of whether liquid biopsies will one day replace surgical biopsies, but when and in what form. First, however, costs need to go down and sensitivity needs to rise.

exosome rna

Adapted from C. B. Meador & C. M. Lovly Nature Med. 21, 663–665 (2015)/M. R. Speicher & K. Pantel Nature Biotechnol. 32, 441–443 (2014) From the article: The tumour trail left in blood

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Chi KR (2016) The tumour trail left in blood. Nature 532(1):269–271. [article]