Availability is not actionability
Study discussant Michael J. Overman, MD, of MD Anderson Cancer Center in Houston, acknowledged that this research substantiates the ability of postoperative ctDNA detection to risk stratify patients with stage III CRC, the predominant stage of participants in the study.
The current results reinforce the researchers’ previously published work (JAMA Oncol. 2019;5[8]:1124-31) and affirm similar findings by other groups (JAMA Oncol. 2019;5[12]:1710-17 and JAMA Oncol. 2019;5[8]:1118-23).
However, Dr. Overman cautioned that “availability is not the same as actionability.”
He also said the “tumor-informed mutation” approach utilized in the Signatera assay differs from the simpler “panel-based” approach, which is also undergoing clinical testing and offers the additional opportunity to test potentially actionable epigenetic targets such as DNA methylation.
Furthermore, the practicality of integrating the tumor-informed mutation approach into the time constraints required in clinical practice was not evaluated in the current analysis.
Dr. Overman pointed out that 16 of the 20 ctDNA-positive patients who received adjuvant chemotherapy sustained a recurrence, so the chemotherapy benefit was lower than expected.
Finally, although ctDNA outperformed CEA in detecting relapse, the greatest impact of ctDNA is its potential to inform the clinician’s decision to escalate and deescalate treatment with impact on survival – a potential that remains unfulfilled.
Next steps
Ms. Henriksen closed her presentation with the perspective that, for serial ctDNA monitoring to be implemented in clinical settings, testing in randomized clinical trials will be needed.
In Denmark, the IMPROVE-IT study is enrolling patients with stage I or low-risk stage II CRC. In this trial, ctDNA-positive patients will receive adjuvant chemotherapy, and ctDNA-negative patients will have longitudinal ctDNA testing but no adjuvant chemotherapy.
A second study, IMPROVE-IT2, will assess the value of ctDNA to direct intensified radiologic surveillance to improve the application of potentially curative treatment for patients with stage II (high-risk) or stage III CRC. Patients with negative ctDNA tests will be followed with longitudinal ctDNA testing only.
In his talk, Dr. Overman highlighted several prospective studies assessing the value of ctDNA testing.
One of these is the ongoing COBRA study (NRG-GI-005), which uses a ctDNA assay (Guardant Lunar-1) for patients with stage IIA CRC for whom standard adjuvant chemotherapy is not indicated.
The patients in COBRA are randomized to active surveillance or assay-directed therapy. Patients assigned to assay-directed therapy have samples analyzed for ctDNA, which would guide the decision about adjuvant chemotherapy. If the postoperative sample is ctDNA positive and the patient accepts adjuvant chemotherapy, the patient could receive one of two standard adjuvant chemotherapy regimens. If ctDNA negative, the patient would be followed with active surveillance alone.
Dr. Overman also highlighted the planned CIRCULATE US trial (NRG-GI008). The aim of this trial is to test intensified adjuvant treatment for stage III CRC patients with positive ctDNA tests. It will employ the Signatera assay.
Ideally, these ongoing trials will provide the evidence base needed for clinicians to optimize adjuvant therapy and surveillance using ctDNA technology.
The current study was sponsored by the Danish Council for Independent Research, The Novo Nordisk Foundation, The Danish Cancer Society, and Natera Inc. Ms. Henriksen disclosed no conflicts of interest. Dr. Overman disclosed relationships with Array BioPharma, Bristol-Myers Squibb, Gritstone Oncology, Janssen, MedImmune, Merck, Novartis, Pfizer, Promega, Roche/Genentech, and Spectrum Pharmaceuticals.
The Gastrointestinal Cancers Symposium is sponsored by the American Gastroenterological Association, the American Society for Clinical Oncology, the American Society for Radiation Oncology, and the Society of Surgical Oncology.
Dr. Lyss was a community-based medical oncologist and clinical researcher for more than 35 years before his recent retirement. His clinical and research interests were focused on breast and lung cancers, as well as expanding clinical trial access to medically underserved populations. He is based in St. Louis. He has no conflicts of interest.