Zosia Chustecka

June 04, 2016

CHICAGO — Instead of invasively obtaining a piece of a tumor — which can be difficult in many cancer types — the 'liquid biopsy' promises to provide similar information from just a drop of blood.

The idea has been around for a few years now, and there are several companies marketing such tests, but how do the results compare with those obtained from conventional tissue biopsies sent to the pathology lab?

They compare rather well, suggest new results released today here at the annual meeting of the American Society of Clinical Oncology (abstract LBA11501; to be presented on Tuesday, June 7).

The test used in this study was Guardant360, which focuses on circulating tumor (ct)DNA and looks for 70 actionable somatic alterations across all solid tumor sites.

Results for the blood test were available for more than 15,000 patients with various cancers — lung (37%), breast (14%), colorectal (10%), and other (38%).

For 386 of these patients, tumor tissue biopsies were also available.

Comparing the two sets of results — from the blood ctDNA test and the tumor tissue — showed good agreement.

"The overall accuracy of ctDNA sequencing in comparison with matched tissue tests was 87% (336/386)," the researchers report.

"This is an emerging area of cancer research," commented Richard Schilsky MD, ASCO chief medical officer and former chief of the section of hematology–oncology at the University of Chicago.

"This lab and many others are now offering these circulating tumor DNA tests. I think commercial use is getting a bit out front of the actual data that demonstrate clinical utility, but there are obvious advantages over tissue-based biopsy," he commented.

Blood is obviously much easier and much safer to obtain than a tumor tissue sample, he said, and generally speaking, the turnaround time is quicker on liquid biopsy than tissue biopsy, so the information is available more rapidly, he said.

Other news released today shows success from a social media experiment. The Metastatic Breast Cancer Project used a website to encourage patients to enroll themselves into a study, which involved submitting a saliva specimen as a source of normal DNA. To the surprise of the researchers, the response was far greater than they had anticipated — more than 1200 women enrolled themselves into this study in the first 3 months (abstract LBA1519; to be presented Monday, June 6).

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