Sustained prognostic impact of circulating tumor cell status and kinetics upon further progression of metastatic breast cancer.

Purpose: Serial longitudinal enumeration of circulating tumor cells (CTCs) has shown its prognostic value on progression-free survival and overall survival (OS) in patients with stage IV breast cancer. This study prospectively evaluated the role of CTCs as a prognostic marker during further progression of metastatic breast cancer (MBC).

Methods: Among 476 MBC patients recruited between 2010 and 2015, the 103 patients with a known CTC status at baseline (CTC) and within 4 weeks of tumor progression (CTC) were included. Progressive disease (PD) was defined according to the Response Evaluation Criteria in Solid Tumors (RECIST, version 1.1). Using the CellSearch method, < 5 and ≥ 5 CTCs per 7.5 ml blood were determined as negative and positive, respectively. A shift in CTC status from baseline to progression ([Formula: see text] to [Formula: see text] and vice versa) was considered as alternating Kinetics.

Results: Median follow-up was 29.9 [21.2, 40.0] months. CTC positivity (37%, n = 38) was associated with a significantly shorter OS than CTC negativity (8.0 [5.1, 10.9] vs 22.6 [15.3, 39.8] months; P < 0.001). Alternating Kinetics was observed in 24% of the patients. This significantly changed the OS prediction of [Formula: see text] patients ([Formula: see text] vs [Formula: see text], 11.4 [9.7, not available (NA)] vs. 7.6 [4.4, 11.5] months; P = 0.044) and [Formula: see text] patients ([Formula: see text] vs. [Formula: see text], 8.4 [4.0, NA] vs. 22.6 [18.9, NA] months, respectively; P < 0.001). Prediction of survival was significantly improved (P = 0.002) by adding CTC status to clinicopathological characteristics and CTC status.

Conclusions: CTC status upon further disease progression is a prognostic factor that could significantly improve well-established models. Thus, it represents a potential additional instrument supporting treatment decision.