A single assessment of the circulating tumor cells (CTC) count before treatment can guide the treatment decision between chemotherapy and single-agent endocrine therapy in ER-positive/HER2-negative metastatic breast cancer, results from the STIC CTC trial showed.
An elevated number of CTC (≥5/7.5 ml) is an adverse prognostic factor for progression-free and overall survival in patients with metastatic breast cancer.1 The phase 3, randomized STIC CTC trial, run before the introduction of CDK4/6 inhibitors for ER-positive/HER2-negative metastatic breast cancer, showed that CTC count was non-inferior to the clinician’s choice—with respect to progression-free survival—to guide first-line treatment selection between chemotherapy and endocrine therapy.2 Prof. François-Clément Bidard (Institut Curie, France) presented the overall survival data (OS) of the STIC CTC trial3 at the 2022 San Antonio Breast Cancer Symposium.
The trial enrolled 755 patients with HR-positive/HER2-negative metastatic breast cancer who could receive either endocrine therapy or chemotherapy as a first-line treatment, according to their physician. In all patients, a baseline CTC count was performed. Patients were randomized to treatment according to physicians’ choice (standard arm) or treatment based on CTC count (CTC arm: endocrine therapy if CTC <5/7.5 ml [CTC-low], chemotherapy if CTC ≥5/7.5 ml [CTC-high]). The median follow-up was 57 months.
In the standard arm, 272 patients with a clinically low-risk profile (Clin-low) were allocated to endocrine therapy and 103 patients with a clinically high-risk profile (Clin-high) to chemotherapy. In the CTC arm, 239 CTC-low patients were allocated to endocrine therapy and 138 CTC-high to chemotherapy. In 463 patients, treatment of physician’s choice was concordant with treatment based on CTC count (Clin-high/CTC-high, Clin-low/CTC-low). In 292 patients, there was discordance between physicians’ choice and treatment based on CTC count (n=189 Clin-low/CTC-high; n=103 Clin-high/CTC-low).
In patients with concordance between physician’s choice and CTC count-based therapy, there was no difference in overall survival between the arms. However, patients with Clin-low/CTC-high treatment based on CTC count (chemotherapy) had a statistically significant and clinically meaningful survival benefit compared with treatment according to physician’s choice (endocrine therapy), with a median OS of 51.8 months versus 35.4 months (HR, 0.53; P=0.001). Therefore, in these patients, chemotherapy should be treatment of first choice. In contrast, patients with Clin-high/CTC-low treatment based on CTC count did not have a different outcome than treatment based on physician’s choice. Therefore, in these patients, endocrine therapy should be treatment of first choice.
Based on these results, Prof. Bidard concluded that “a single assessment of the CTC count before the start of treatment can guide the treatment decision between chemotherapy and single-agent endocrine therapy in ER-positive/HER2-negative metastatic breast cancer.”
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