Study details
In his presentation, Dr. Bidard explained that CTC count is an FDA-approved standardized liquid biopsy biomarker, with a count of greater than or equal to 5 cells per 7.5 mL of blood deemed an adverse prognostic marker, regardless of the line of therapy, with a grade 1 level of evidence.
Previous studies have indicated that a high CTC count is strongly associated with overall survival, at a hazard ratio of 2.78.
Crucially, the CTC count “complements” and does not duplicate standard clinicopathological prognostic factors, Dr. Bidard said.
To determine the potential of the CTC count as an aid to treatment decisions, Dr. Bidard and colleagues conducted a trial in pre- and postmenopausal women with untreated HR+/HER2- metastatic breast cancer who were able to receive either endocrine therapy or chemotherapy.
They were randomly assigned to either a standard group, in which the treatment decision followed the physician’s choice, regardless of their CTC count, or to a CTC group, in which the physicians made a treatment recommendation but the choice was driven by the CTC count.
Dr. Bidard reminded the audience that the primary endpoint of PFS to demonstrate the non-inferiority of CTC versus physician treatment decisions has already been met, with the results published in 2020. Those results came from an analysis of 788 patients enrolled between February 2012 and July 2016 at 17 sites in France and showed after 42 months of follow-up that the median PFS in the CTC arm was 15.6 months versus 14 months in the physician choice arm, at a hazard ratio of 0.92.
The current pre-planned analysis involved 755 patients who were followed up for a median of 57 months by the time the trial was stopped in 2021.
In the standard treatment arm, endocrine therapy was favored by physicians in 72.7% of cases (Clin-low), while 27.3% were given chemotherapy (Clin-high).
In the CTC group, 73.5% of patients were recommended to have endocrine therapy by their physician based on their clinical characteristics (Clin-low), whereas 26.5% were suggested to have chemotherapy (Clin-high).
In contrast, 60.1% of patients in the standard arm would have received endocrine therapy based on their CTC count (CTC-low), and 39.9% chemotherapy (CTC-high), while 63.4% of those in the CTC arm were given endocrine therapy based on their CTC count (CTC-low), and 36.6% were assigned to chemotherapy (CTC-high).
Once the allocated treatment was known in both treatment groups, the physicians were free to choose between endocrine therapy (mostly a single-agent aromatase inhibitor or fulvestrant) and chemotherapy (mostly paclitaxel or capecitabine).
Although CDK4/6 inhibitors were not approved at the time of enrollment, 42.2% of patients across both treatment groups received one of these drugs as a second-line or later therapy.
Guiding treatment decisions
Dr. Bidard said that, overall, more patients in the CTC arm were assigned to chemotherapy, at a difference of 9.7%. There was approximately 60% concordance between physician- and CTC-guided treatment choices; in other words, patients were recommended the same treatment by the two approaches in both treatment groups.
In these patients, there was no significant difference in overall survival between the physician choice and CTC groups, at a median of 45.5 months versus 51.3 months (hazard ratio, 0.85; P = .11).
The updated PFS data revealed a median PFS of 15.7 months in the CTC group versus 13.8 months, again at a nonsignificant HR of 0.94.
These results, Dr. Bidard said, indicate that CTC-based treatment choices are “safe.”
However, there was discordance between physician and CTC-based treatment choices in around 40% of cases, meaning that the two approaches recommended different therapies.
The physician recommended endocrine therapy, in contrast to the CTC count indicating chemotherapy, in 25% of patients (Clin-low/CTC-high), whereas 13.6% of cases were recommended chemotherapy while their CTC count indicated otherwise (Clin-high/CTC-low).
In Clin-low/CTC-high patients, this resulted in 26.1% of patients in the standard group receiving endocrine therapy when their CTC count indicated chemotherapy, while 23.9% of patients in the CTC group received chemotherapy even though their physician did not recommended it.
Comparing these two groups, the researchers found that patients in the CTC group had a significantly longer PFS, at 15.7 months versus 10 months (HR, 0.65; P = .005). They also had a significantly longer median overall survival, at a median of 51.8 months versus 35.4 months with physician choice (HR, 0.53; P = .001).
Among Clin-high/CTC-low, there was no benefit from physician’s choice of chemotherapy over the CTC-guided recommendation of endocrine therapy, at an HR for PFS of 1.14 for CTC- versus physician-guided therapy (P = .54), and an HR for overall survival of 0.88 (P = .64).
Dr. Bidard highlighted that the treatment effects were seen across prespecified subgroups.
The study was funded by the Institut National du Cancer, the Institut Curie SIRIC2 program, and Menarini Silicon Biosystems. Dr. Chan reports no relevant financial relationships. Dr. Hayes and Dr. Bidard reported relationships with numerous pharmaceutical companies.
A version of this article first appeared on Medscape.com.