SAN ANTONIO – When choosing between chemotherapy and endocrine therapy for patients with hormone receptor (HR)+/HER2- metastatic breast cancer, allowing the results from a blood test that measures circulating tumor cell (CTC) count to overrule physician’s choice of therapy can significantly improve overall survival.
But One expert reacting to the findings says probably not, and another pointed out that the CTC count test used in the trial (CellSearch), although approved by the Food and Drug Administration, is not widely used in clinical practice.
The findings comes from updated results from the STIC CTC study.
“When the trial was designed, the question related to the choice between single-agent endocrine therapy and chemotherapy [in] first-line therapy,” explained study presenter François-Clément Bidard, MD, PhD, professor of medical oncology at Institut Curie and Versailles Saint-Quentin University, Paris.
Since then, the first-line treatment has changed and can now can also include cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, but Dr. Bidard said the results are still clinically relevant.
Nowadays, endocrine therapy plus CDK4/6 inhibitors is the “preferred option for treatment-naive patients, but the dilemma between endocrine therapy and chemotherapy remains after disease progression on adjuvant or first-line therapy with CDK4/6 inhibitors, where current guidelines advocate in favor of endocrine therapy, despite its short-lived efficacy.”
“In that scenario, based on the STIC CTC trial results, the CTC count in combination with predictive biomarkers, whenever available, may help customize the early use of chemotherapy or antibody-drug conjugates, which are becoming more and more attractive,” Dr. Bidard said.
The research was presented here at the San Antonio Breast Cancer Symposium (SABCS).
The study involved more than 750 patients with HR+/HER2- metastatic breast cancer randomly assigned to physician choice or CTC-guided therapy, although the physician decision and the recommendation based on the CTC count was recorded in both groups.
Using the CellSearch (Menarini Silicon Biosystems) to perform the CTC count at baseline only, the team defined patients as low or high risk, with low-risk patients deemed to need only endocrine therapy and high-risk patients recommended chemotherapy.
Physicians based their decisions on current guidelines and their clinical experience.
In the 25% of cases where CTC count would recommend chemotherapy while the physician would recommend endocrine therapy, following the CTC count–based choice resulted in a 35% improvement in progression-free survival (PFS) and a 47% increase in overall survival.
In all other situations, including those when the CTC count recommended endocrine therapy in contrast to the physicians, or the approximately 60% of cases in which the two were in agreement, there was no difference in survival outcomes between the approaches.
Reacting to the findings, Nancy Chan, MD, medical oncologist and the director of breast cancer clinical research at NYU Langone’s Perlmutter Cancer Center, said that the “goal is really to understand how we can personalize treatment options for patients.”
Another aim is to avoid performing a tumor biopsy, if possible, “as that has increased morbidity for patients.”
She noted also that choosing between endocrine therapy and chemotherapy is a “big decision.” These researchers “really wanted to help some patients get less chemotherapy,” as they felt that “some patients are getting too much” as they are not really that high risk and should get endocrine therapy instead.
However, Dr. Chan said that the CTC count is a “complicated concept” and is “not something we’re all using in our clinical practice yet.”
With regard to the approximately 40% discordance between the CTC- and physician-guided choices, Dr. Chan said that clinicians are perhaps not as accurate as they believed in predicting risk when relying on the clinical or pathological features of the tumor.
On Twitter, Guilherme Nader-Marta, MD, Jules Bordet Institute, Université Libre de Bruxelles, Belgium, commented that the question behind the study was whether CTC measurement is a “clinically useful strategy for first-line treatment decision-making.”
“Amazingly,” he continued, the trial went “straight to the point” to answer the question and showed that CTC-based decisions can offer a survival benefit.
Daniel F. Hayes, MD, co-director of the Breast Oncology Program at the University of Michigan Comprehensive Cancer Center, Ann Arbor, echoed these thoughts, saying that the goals of therapy are to make patients live longer and “better.”
He said that the point of any clinical biomarker is not only to show that testing for it offers “analytical validity” but that it also provides “clinical utility” in that it can guide treatment decisions to improve outcomes.
Dr. Hayes, who was not involved in the study but has worked for many years on the development of CellSearch, said that the results do not make it clear whether measuring CTC counts meets the definition of clinical utility, but it’s “very close.”
On the other hand, the analytical validity of the test is “excellent,” and, in that context, was well-chosen, he said, adding that the endpoint of the trial “is the one most important to us: improvement in overall survival.”
Dr. Hayes noted that the magnitude of benefit from CTC-guided therapy was “moderate,” although that is a “matter of perception,” and the “level of evidence is probably 2 or 3.” Although the trial was prospective, he said, the key results were in a “relatively small” subgroup.
The question is, Dr. Hayes continued: “Is this enough to change practice? My conclusions are: probably not.”
Although patients rated as low risk based on their low CTC count avoided chemotherapy, “it’s not clear to me that this whole thing is sufficient for clinical utility in context of what we know today.” The key issue, however, is who decides whether CTC counts are measured and whether they will be used to guide therapy decisions – will it be the patient, the caregiver, an expert guidelines panel, or third party payers/society?