Circulating tumor cells (CTC) in blood are promising new biomarkers potentially useful for prognostic prediction and monitoring of therapies in patients with solid tumors including colon cancer. Moreover, CTC research opens a new avenue for understanding the biology of metastasis in patients with cancer. However, an in-depth investigation of CTCs is hampered by the very low number of these cells, especially in the blood of patients with colorectal cancer. Thus, the establishment of cell cultures and permanent cell lines from CTCs has become the most challenging task over the past year. Here, we describe, for the first time, the establishment of cell cultures and a permanent cell line from CTCs of one patient with colon cancer. The cell line designated CTC-MCC-41 has been cultured for more than one year, and the cells Ó2015 AACR.

Immune checkpoint regulators such as PD-L1 have become exciting new therapeutic targets leading to long lasting remissions in patients with advanced malignancies. However, in view of the remarkable costs and the toxicity profiles of these therapies, predictive biomarkers able to discriminate responders from non-responders are urgently needed. In the present paper, we provide evidence that PD-L1 is frequently expressed on metastatic cells circulating in the blood of hormone receptor-positive, HER2-negative breast cancer patients. We performed western blot, flow cytometry and immunocytochemical analyses to demonstrate the specificity of the PDL1 antibody used in our study and established immunoscores for PDL1 expression on single tumor cells. We then selected sixteen patients with circulating tumor cells (CTCs) using the CellSearch(®) system and found PD-L1((+)) CTCs in 11 patients (68.8%). The fraction of PD-L1((+)) CTCs varied from 0.2 to 100% in individual patients. This is the first report demonstrating the expression of PD-L1 on CTCs. The established CTC/PD-L1 assay can be used for liquid biopsy in future clinical trials for stratification and monitoring of cancer patients undergoing immune checkpoint blockade.

IMPORTANCEThe choice between chemotherapy and endocrine therapy as first-line treatment for hormone receptor-positive, ERBB2 (also known as HER2)-negative metastatic breast cancer is usually based on the presence of clinical features associated with a poor prognosis. In this setting, a high circulating tumor cell (CTC) count (Ն5 CTCs/7.5 mL) is a strong adverse prognostic factor for overall survival and progression-free survival (PFS).OBJECTIVE To compare the efficacy of a clinician-driven treatment choice vs a CTC-driven choice for first-line treatment. INTERVENTIONSIn the CTC arm, patients received chemotherapy or endocrine therapy according to the CTC count (chemotherapy if Ն5 CTCs/7.5 mL; endocrine therapy if <5 CTCs/7.5 mL), whereas in the control arm, the choice was left to the investigator. DESIGN, SETTING, AND PARTICIPANTSIn the STIC CTC randomized, open-label, noninferiority phase 3 trial, participants were randomized to a clinician-driven choice of first-line treatment or a CTC count-driven first-line treatment choice. Eligible participants were premenopausal and postmenopausal women 18 years or older diagnosed with hormone receptor-positive, ERBB2-negative metastatic breast cancer. Data were collected at 17 French cancer centers

Functional studies giving insight into the biology of circulating tumor cells (CTCs) remain scarce due to the low frequency of CTCs and lack of appropriate models. Here, we describe the characterization of a novel CTC‐derived breast cancer cell line, designated CTC‐ITB‐01, established from a patient with metastatic estrogen receptor‐positive (ER+) breast cancer, resistant to endocrine therapy. CTC‐ITB‐01 remained ER+ in culture, and copy number alteration (CNA) profiling showed high concordance between CTC‐ITB‐01 and CTCs originally present in the patient with cancer at the time point of blood draw. RNA‐sequencing data indicate that CTC‐ITB‐01 has a predominantly epithelial expression signature. Primary tumor and metastasis formation in an intraductal PDX mouse model mirrored the clinical progression of ER+ breast cancer. Downstream ER signaling was constitutively active in CTC‐ITB‐01 independent of ligand availability, and the CDK4/6 inhibitor Palbociclib strongly inhibited CTC‐ITB‐01 growth. Thus, we established a functional model that opens a new avenue to study CTC biology.