Prognostic impact of circulating tumor cell apoptosis and clusters in serial blood samples from patients with metastatic breast cancer in a prospective observational cohort

Abstract

BackgroundPresence of circulating tumor cells (CTCs) is a validated prognostic marker in metastatic breast cancer. Additional prognostic information may be obtained by morphologic characterization of CTCs. We explored whether apoptotic CTCs, CTC clusters and leukocytes attached to CTCs are associated with breast cancer subtype and prognosis at base-line (BL) and in follow-up (FU) blood samples in patients with metastatic breast cancer scheduled for first-line systemic treatment.MethodsPatients with a first metastatic breast cancer event were enrolled in a prospective observational study prior to therapy initiation and the CellSearch system (Janssen Diagnostics) was used for CTC enumeration and characterization. We enrolled patients (N = 52) with ≥5 CTC/7.5 ml blood at BL (median 45, range 5–668) and followed them with blood sampling for 6 months during therapy. CTCs were evaluated for apoptotic changes, CTC clusters (≥3 nuclei), and leukocytes associated with CTC (WBC-CTC, ≥1 CTC + ≥1 leukocytes) at all time-points by visual examination of the galleries generated by the CellTracks Analyzer.ResultsAt BL, patients with triple-negative and HER2-positive breast cancer had blood CTC clusters present more frequently than patients with hormone receptor-positive cancer (P = 0.010). No morphologic characteristics were associated with prognosis at BL, whereas patients with apoptotic CTCs or clusters in FU samples had worse prognosis compared to patients without these characteristics with respect to progression-free (PFS) and overall survival (OS) (log-rank test: P = 0.0012 or lower). Patients with apoptotic or clustered CTCs at any time-point had impaired prognosis in multivariable analyses adjusting for number of CTCs and other prognostic factors (apoptosis: HROS = 25, P < 0.001; cluster: HROS = 7.0, P = 0.006). The presence of WBC-CTCs was significantly associated with an inferior prognosis in terms of OS at 6 months in multivariable analysis.ConclusionsPatients with a continuous presence of apoptotic or clustered CTCs in FU samples after systemic therapy initiation had worse prognosis than patients without these CTC characteristics. In patients with ≥5 CTC/7.5 ml blood at BL, morphologic characterization of persistent CTCs could be an important prognostic marker during treatment, in addition to CTC enumeration alone.Clinical Trials (NCT01322893), registration date 21 March 2011Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2406-y) contains supplementary material, which is available to authorized users.

Circulating tumor cell clusters: What we know and what we expect (Review)

“…One such study enrolled 97 patients with SCLC and found that 32% of patients were positive for CTC clusters, and the presence of CTC clusters at baseline indicated shorter progression-free survival and overall survival (11). An additional prognostic value of CTC clusters in patients with elevated CTCs were reported in two prospective cohorts of advanced stage or metastatic breast cancer (78,79). Furthermore, information regarding CTC clusters were indicative of the failure of chemotherapy treatments in colorectal cancer (60).…”

Tracking cancer progression: from circulating tumor cells to metastasis

“…Although they typically represent a minority of the CTCs found in the peripheral circulation, they have a metastatic potential that has been estimated to be 23 to 50 times greater than that of their single-cell counterparts [21]. In addition, the presence of CTC clusters and cluster size are associated with worse clinical outcome than the presence of single CTCs in multiple cancer types [17,21,[47][48][49][50]. Although the existence of CTC clusters has been known for decades [51][52][53][54][55], the biological mechanisms behind their formation, survival, dissemination, and superior metastatic ability are only partially understood [48].…”

Liquid biopsies

“…In patients with ≥5 CTC/7.5 mL blood at baseline, morphologic characterization of persistent CTCs could be an important prognostic marker during treatment, in addition to CTC enumeration alone. 52 It was also recently reported that mitotic CTCs are relativity common in aggressive late-stage breast cancer and may significantly correlate with shortened OS. 53 Many studies so far have confirmed a lack of concordance in HER2 status between tumor tissue and CTCs that may be correlated with the time interval between tissue and CTC HER2 testing.…”

“…Patients with a continuous presence of apoptotic or clustered CTCs in follow‐up samples after systemic therapy initiation had worse prognosis than patients without these CTC characteristics. In patients with ≥5 CTC/7.5 mL blood at baseline, morphologic characterization of persistent CTCs could be an important prognostic marker during treatment, in addition to CTC enumeration alone . It was also recently reported that mitotic CTCs are relativity common in aggressive late‐stage breast cancer and may significantly correlate with shortened OS …”