Caution required with new tests

Caution required with some very new tests designed to assist cancer treatment.

The FoundationOne (F1; Foundation Medicine) and the Guardant360 (G360; Guardant Health) are tests that sequence particular genes from cancers and give information to assist the requesting doctor to choose particular treatment options, especially in patients with advanced cancer where standard therapies have failed. The F1 test sequences clinical tumour cell samples from a biopsy or excision to characterize the exons of 315 cancer-associated genes and introns from 28 genes involved in rearrangements. The G360 test uses cell-free circulating DNA from blood to sequence 70 genes. These tests are not widely used in Australia at present because access to expensive new cancer drugs here is based on specific criteria for each drug. However they are examples of the new commercial tests being offered in this area in other countries. 

Investigators in Washington State in the US looked at just nine patients with a variety of different cancers all of whom had both tests done. They then compared the results and treatment recommendations from the two tests for each patient. Normally such a small study would not attract much attention but the results were so striking that doctors are interested. Their research letter was published online December 15 in JAMA Oncology.

The results can be summarized as follows: All 9 patients (5 with breast cancer and 4 others with pancreatic, lung, salivary gland, and thymic cancers, respectively) had both tests. The investigators limited comparisons to alterations identifiable by both F1 and G360 testing. The genomic alterations reported by each test were compared for each patient. And the results were also assessed to compare the recommended drugs.

  • One patient had no genetic alteration identified by using either platform. The other 8 patients had 45 alterations, but only 10 (22%) were concordant between the platforms. In other words, the majority of the test results were discordant. For 2 of these 8 patients, there was zero concordance among the described alterations.
  • For the 8 patients, a total of 36 drugs were recommended. Only 9 drugs (25%) were recommended for the same patients by both platforms, and in 5 patients, there was no overlap between the drugs recommended by the F1 test and those recommended by the G360 test. So, in the majority of the patients, there was zero concordance in terms of drug recommendations.

Dr. Vinay Prasad, MD, from the Oregon Health and Sciences University in Portland was asked for comment by Medscape Medical News; "What we are talking about here is precision oncology — the use of sequencing in patients with a range of cancers who have exhausted other options in order to pair them with therapies. A very basic question about this approach has been: Would two different tests give the same result? A high level of concordance is a prerequisite to the tests being of any clinical use." 

Dr Prasad believes that these genetic tools should ultimately be required to prove that they improve outcomes — namely, overall survival, because that is the standard for other cancer practices. "These tests have no credible evidence they make people better off," he said.

Previously, critics of the mushrooming industry of cancer genetics testing in the context of treatment decision making have called for clinical trials to determine whether they actually improve outcomes. This study will add fuel to their call for such trials.

Further Reading
JAMA abstract
Journal of Clinical Pathways

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