High CTC Count Favors Chemotherapy in First-Line ER+, HER2- Metastatic Breast Cancer

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There is currently no predictive biomarker to aid the decision of whether to treat with chemotherapy or hormone therapy for patients with ER-positive metastatic breast cancer.
There is currently no predictive biomarker to aid the decision of whether to treat with chemotherapy or hormone therapy for patients with ER-positive metastatic breast cancer.
The following article features coverage from the San Antonio Breast Cancer Symposium (SABCS) 2018 meeting. Click here to read more of Cancer Therapy Advisor's conference coverage.

Higher circulating tumor cell (CTC) level is associated with a better response to chemotherapy compared with endocrine therapy, according to data from the STIC CTC trial presented at the 2018 San Antonio Breast Cancer Symposium in San Antonio, Texas.1

There is currently no predictive biomarker to aid the decision of whether to treat with chemotherapy or hormone therapy for patients with estrogen receptor (ER)-positive metastatic breast cancer. CTC count has previously been established as a strong prognostic marker in this population. The purpose of this study was to evaluate CTC count using the tool CellSearch.

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The multicenter, phase 3, noninferiority STIC CTC trial enrolled 778 patients with hormone receptor-positive, HER2-negative metastatic breast cancer to receive first-line treatment with chemotherapy or endocrine therapy. The choice of treatment was by random assignment, selected by clinically-driven choice or CTC-driven choice (CTC count not disclosed, HT or CT administered as decided a priori). In the CTC count arm, patients with low CTC levels (as defined as < 5 CTC/7.5 mL) received endocrine therapy, whereas patients with high CTC levels (as defined as ≥ 5 CTC/7.5 mL) received chemotherapy.

The primary end point was progression-free survival (PFS) and the secondary end points included overall survival (OS) and prespecified subgroup analyses.

The CTC count was noninferior to the clinician's choice arms for PFS, with a median of 15.6 months (95% confidence interval [CI], 12.8-17.3) compared with 14.0 months (95% CI, 12.2-16.0) in the clinician's choice arm (hazard ratio [HR], 0.92; 90% CI, 0.80-1.06), based on the prespecified noninferiority margin of 1.25. 

OS was similar between arms, with a 2-year rate of 82.1% in the CTC count arm compared with 81.4% in the clinician's choice arm.

CTC count confirmed clinician's choice in 67% of patients who received endocrine therapy and 48% of patients who received chemotherapy. For discordant cases, CTC count that differed from clinician's choice resulted in a switch in therapy. In these cases, patients who were switched to chemotherapy demonstrated a significantly prolonged PFS compared with endocrine therapy (median, 15.5 months vs 10.5 months). There was a trend toward improved OS with chemotherapy versus endocrine therapy based on CTC count (median, 42.0 vs 37.1 months). Patients who were switched to endocrine therapy based on low CTC count demonstrated no difference in PFS between arms.

The authors concluded that high CTC count favors chemotherapy compared with endocrine therapy. As a result, the authors stated in a press release that, “CTC count should be included in the decision algorithm for HR-positive, HER2-negative metastatic breast cancer patients.”2

Read more of Cancer Therapy Advisor's coverage of the SABCS 2018 meeting by visiting the conference page.

References

  1. Bidard FC, Jacot W, Dureau S, et al. Clinical utility of circulating tumor cells (CTC) count to choose between 1stline hormone therapy & chemotherapy in ER+ HER2- metastatic breast cancer. Presented at: 2018 San Antonio Breast Cancer Symposium; San Antonio, TX: December 4-8, 2018. Abstract GS3-07.
  2. Cavallo J. Circulating Tumor Cell Count Could Help Choose Treatment for Metastatic Breast Cancer Patients. 2018 SABCS press release. http://www.ascopost.com/News/59547. Published December 6, 2018. Accessed December 6, 2018. 

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