Circulating tumor cell count could be used to determine treatment of metastatic breast cancer

Abstract

© R O M A SE T / S H U TT ER ST O C K .C O M T he circulating tumor cell (CTC) count could help to determine which type of frontline therapy would be best for patients with 2 different types of metastatic breast cancer, a new study finds. The research, from the large phase 3 randomized trial STIC CTC, was presented at the 2018 San Antonio Breast Cancer Symposium, which was held December 4 – 8, 2018. Lead author François-Clément Bidard, MD, PhD, a professor of medical oncology at the Curie Institute in Saint-Cloud, France, and the University of Versailles, notes that hormone therapy and chemotherapy are the main first-line treatment choices for patients newly diagnosed with ER-positive or HER2-negative metastatic breast cancer. Those treatments then are followed by maintenance hormone therapy. Currently, to the authors’ knowledge, no biomarkers exist to help guide clinicians in making the choice between the 2 treatments, he adds. Because of its limited side effects, frontline hormone therapy often is the preferred treatment choice; however, chemotherapy often is suggested in patients with poor prognoses, according to Dr. Bidard. Nevertheless, the decision is not always clear, and different physicians may have conflicting recommendations for the same patient, he says. Previous studies that have investigated the CTC count in thousands of patients with breast cancer have shown that it is the best prognostic marker for both patients with ER-positive and HER2-negative, stage IV breast cancer, according to Dr. Bidard. To determine whether the CTC count could be used to guide treatment choices in this population, Dr. Bidard and his colleagues analyzed 778 patients who were randomly assigned to either a clinically driven arm (in which therapy was decided by a physician based on clinical factors) or a CTC-driven arm. In the latter, hormone therapy was administered if 7.5 mL of blood had <5 CTCs and chemotherapy was given if 7.5 mL of blood had ≥5 CTCs. In the majority of cases, the CTC count did confirm the clinical choice. However, in divergent cases, findings indicated that the CTC count can be trusted when considering either escalating or de-escalating frontline therapy. Specifically, the researchers demonstrated that basing the treatment decision on the CTC count alone did not harm patients in the overall study population. In addition, if treatment recommendations diverged based on clinician recommendation versus the CTC count, the choice of chemotherapy was associated with a significant 35% decrease in the risk of death, according to Dr. Bidard. The findings also indicated that patients whose treatment was escalated to chemotherapy based on the CTC count had a significantly longer progression-free survival and a trend toward a longer overall survival. At the same time, patients whose treatment was de-escalated to hormone therapy based on the CTC count did not have a significantly shorter survival compared with those with a low CTC count who received chemotherapy in the clinically driven arm. In the group with divergent treatment recommendations, overall survival rates at 24 months were 82.9% in those patients treated with chemotherapy (later followed by hormone therapy) compared with 74.7% in patients treated with frontline hormone therapy. The findings led Dr. Bidard and his colleagues to conclude that using the modern prognostic biomarker of CTC count may lead to better patient survival. One limitation, he notes, is that during the study follow-up period, physicians began to use a new type of frontline treatment, the CDK4/6 inhibitors palbociclib, ribociclib, and abemaciclib, for patients with metastatic breast cancer, and it was not included in the study.