Changes in ctDNA levels predict patient survival
The researchers found that patients who experienced a greater than 90% decline in ctDNA levels by the third treatment cycle had significantly longer overall survival (OS) than those with less than 90% ctDNA decline or any increase. According to data presented by Dr. Kurzrock, the median OS was not reached in the group with greater than 90% decline in on-treatment ctDNA levels, versus 9.4 months in the group with less than 90% decline or ctDNA increase (P = .007). These findings held true when the analysis was limited to the 14 patients with colorectal cancer, in which median OS was not reached in the group with greater than 90% decline in on-treatment ctDNA levels, versus 10.2 months in the group with less than 90% decline or ctDNA increase (P = 0.04).
Notably, the prognostic significance of ctDNA changes remained even among patients exhibiting radiographic stable disease, underscoring the limitations of relying solely on anatomic tumor measurements and highlighting the potential for ctDNA monitoring to complement standard clinical assessments. In the subset of patients with radiographic stable disease, those with a greater than 90% ctDNA decline had significantly longer OS than those with less ctDNA reduction (not reached versus 9.4 months; P = .01).
“When used as a complement to imaging, tissue-informed ctDNA monitoring with FoundationOne Tracker can provide more accuracy than imaging alone,” Dr. Kurzrock noted in an interview.
Dr. Kasi echoed Dr. Kurzrock’s enthusiasm regarding the clinical usefulness of these findings, saying, “Not only can you see very early on in whom the ctDNA is going down and clearing, but you can also tell apart within the group who has ‘stable disease’ as to who is deriving more benefit.”
The researchers also observed that increases in on-treatment ctDNA levels often preceded radiographic evidence of disease progression by a median of 1.3 months. These findings highlight the potential for ctDNA monitoring to complement standard clinical assessments, allowing us to detect treatment response and disease progression earlier than what is possible with imaging alone, Dr. Kurzrock explained during her talk. “This early warning signal could allow clinicians to intervene and modify treatment strategies before overt clinical deterioration,” she said.
In an interview, Dr. Kasi highlighted that this high sensitivity and specificity and the short half-life of the tumor-informed ctDNA assay make this liquid biopsy of great clinical value. “The short half-life of a few hours means that if you do an intervention to treat cancer with HER2-directed therapy, you can very quickly assess response to therapy way earlier than traditional radiographic methods.”
Dr. Kasi cautioned, however, that this assay would not capture whether new mutations or HER2 loss occurred at the time of resistance. “A repeat tissue biopsy or a next-generation sequencing-based plasma-only assay would be required for that,” he said.
Implementation of ctDNA monitoring in clinical trials
Dr. Kurzrock acknowledged that further research is needed to validate these results in larger, prospective cohorts before FoundationOne Tracker is adopted in the clinic. She noted, however, that this retrospective analysis, along with results from previous studies, provides a rationale for the use of ctDNA monitoring in clinical trials.
“In some centers like ours, ctDNA monitoring is already part of our standard of care since not only does it help from a physician standpoint to have a more accurate and early assessment of response, but patients also appreciate the information gained from ctDNA dynamics,” Dr. Kasi said in an interview. He explained that when radiographic findings are equivocal, ctDNA monitoring is an additional tool in their toolbox to help guide care.
He noted, however, that the cost is a challenge for implementing ctDNA monitoring as a complementary tool for real-time treatment response monitoring. “For serial monitoring, helping to reduce costs would be important in the long run,” he said in an interview. He added that obtaining sufficient tissue for testing using a tumor-informed assay can present a logistical challenge, at least for the first test. “You need sufficient tissue to make the barcode that you then follow along,” he explained.
“Developing guidelines through systematic studies about testing cadence would also be important. This would help establish whether ctDNA monitoring is helpful,” Dr. Kasi said in an interview. He explained that in some situations, biological variables affect the shedding and detection of ctDNA beyond the assay — in those cases, ctDNA monitoring may not be helpful. “Like any test, it is not meant for every patient or clinical question,” Dr. Kasi concluded.
Dr. Kurzrock and Dr. Kasi reported no relationships with entities whose primary business is producing, marketing, selling, reselling, or distributing healthcare products used by or on patients.