CHICAGO — Circulating tumor DNA (ctDNA) can predict relapse risk in some cases of early, high-risk breast cancer, but it’s too soon to use it to guide adjuvant therapy decisions, according to a study presented at the American Society of Clinical Oncology annual meeting.
Detectable ctDNA is “highly prognostic of worse outcomes, particularly in patients who [remain] persistently positive,” but the correlation isn’t perfect, said lead investigator Sherene Loi, MMBS, PhD, a breast cancer specialist at the Peter MacCallum Cancer Centre in Melbourne, Australia.
Although less likely, relapses also occurred in the study among women without ctDNA elevation. Conversely, there were women with elevated ctDNA who did not relapse, she said. The study was a subanalysis of the monarchE trial of adjuvant abemaciclib, a CDK 4/6 inhibitor.
Eventually, “we would like to use” ctDNA to guide adjuvant treatment decisions, but the research isn’t there yet, Dr. Loi said. It’s possible, for instance, that persistently detectable ctDNA indicates early treatment failure and the need for treatment intensification. Future research should tackle the issue.
Study discussant Francois-Clement Bidard, MD, PhD, a breast cancer specialist at Institut Curie, Paris, agreed that ctDNA isn’t ready for primetime in adjuvant early, high-risk breast cancer.
“There is no clinical evidence to suggest that there is clinical utility in this setting. There are several trials that are ongoing,” he said, but for now “you shouldn’t,” for example, “use ctDNA to de-escalate adjuvant CDK4/6 [inhibitors]. It could be in the future that we could have data on this, but at the moment, [the] clear clinical message [is] no way.”
At 5-year follow-up, the monarchE trial found a 7.6% invasive disease-free survival (IDFS) improvement when abemaciclib was added to the first 2 years of endocrine therapy in women with HR+, HER2-, node positive, high-risk early breast cancer. The combination is now a standard adjuvant option for the disease.
The ctDNA study focused on a subset of 910 subjects with adequate ctDNA testing to run the analysis. The study population was also selected to be enriched for overall IDFS events (27% versus 18% across the trial’s 5,637 subjects). An IDFS event was defined as a local, regional, contralateral or distant invasive recurrence; a new primary tumor; or death from any cause.
Testing was performed using the Signatera ctDNA assay. Baseline samples were taken after completion of adjuvant chemotherapy, then again at 3, 6, or 24 months.
Overall, ctDNA detection was infrequent. Just 8% of patients were positive at baseline and 17% were positive at any point during the trial. Even so, ctDNA detection at any point was adversely prognostic.
Patients who were ctDNA positive at baseline were more likely to experience an IDFS event, compared with those who were ctDNA negative at baseline (80% at 4 years follow-up versus 23%).
Similarly, those who remained positive or became positive during testing were more likely to experience an IDFS event compared with those who became negative or remained negative throughout testing.
For instance, all 34 patients who were positive at baseline and remained positive had an IDFS event by year 4, versus just 40% who started positive but then cleared their ctDNA.
Among women who were negative at baseline and remained negative, 13% had an IDFS event versus 89% who started negative but then turned positive. Subjects who turned positive also had the shortest time to an IDFS event, a median of 7 months.
Among women who recurred, those who were ctDNA negative tended to have local, regional, or contralateral recurrences, while ctDNA positive patients tended to have distant recurrences.
The finding “really highlights that ctDNA antedates the metastatic clinical relapse. What the ctDNA is telling you is that the metastatic process has been completed, and metastases are about to grow,” Dr. Bidard said.
The work was funded by Eli Lilly, maker of abemaciclib, with collaboration from Natera, maker of the Signatera assay. Dr. Loi is an adviser and researcher for Lilly, among other industry ties. Dr. Bidard is a speaker and consultant for Lilly, among other ties.
