Circulating Tumor Cell Count Is A Promising Biomarker For Guiding Breast Cancer Treatment

Circulating tumor cell (CTC) count may be an effective biomarker for deciding between chemotherapy and endocrine therapy for hormone receptor-positive, ERBB2-negative metastatic breast cancer, according to new results from a randomized clinical trial.

In this trial, which was published in JAMA Oncology, a high CTC count (≥5 CTCs/7.5 mL) in patients’ blood was found to be a strong adverse prognostic factor for overall survival (OS) and progression-free survival (PFS).

The randomized phase III STIC CTC trial enrolled 778 patients with stage 4 ER+, HER2- breast cancer. Participants were randomized to either a physician-selected treatment group based on clinical factors, or to a CTC-driven treatment group. In the CTC group, patients with a tumor circulation count of 5 CTCs/7.5 mL or more received chemotherapy, and those with less than 5 CTCs/7.5 mL received hormone therapy. Menarini Silicon Biosystems’ CELLSEARCH CTC System was utilized to measure CTC count in all participants. The study’s primary end point was PFS, with a noninferiority margin of 1.25 for the hazard ratio.

Among 755 patients in the per-protocol population, 37% of the physician-selected arm and 27% of the CTC-driven arm received chemotherapy. Median PFS was 15.5 months (95% CI, 12.7-17.3) in the CTC arm and 13.9 months (95% CI, 12.2-16.3) in the physician-selected arm. The hazard ratio was 0.94 (90% CI, 0.81-1.09)., meaning the noninferiority endpoint was met.

CTC count correlated with clinical decisions for most patients in the physician-selected treatment group. In the CTC-driven cohort, chemotherapy for patients with high CTC count significantly improved progression free survival (PFS), while de-escalation to hormone therapy for those with low CTC count did not have a detrimental impact on PFS or OS.

“Based on our research, the use of the CTC count represents the first objective and reproducible decision tool to help physicians choose between hormone therapy or chemotherapy for this particular group of patients,” lead author Francois-Clement Bidard, MD, PhD, Professor of Medical Oncology at Institut Curie and University of Versailles, said in a press release. “The CTC count complements but does not duplicate the physician’s opinion on which treatment to choose and should be included in the decision algorithm. This CTC test may help customizing treatment decisions for all women suffering from ER+ HER2- metastatic breast cancer.”