Biological and Clinical Significance of Circulating Tumor Cells in Breast Cancer

Fina, Emanuela (2017). Biological and Clinical Significance of Circulating Tumor Cells in Breast Cancer. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000c141

Abstract

Circulating tumor cells (CTCs) represent a unique source of information that might help clarifying numerous aspects of metastasis biology and finding new clinically relevant biomarkers. On the hypothesis that CTCs possess a distinct profile compared to solid primary and secondary lesions, the transcriptome of experimentally-derived CTCs was compared with those of the primary tumor (PT) and metastases at lymph-nodes (LNs) and lung, in order to identify CTC specific signatures involved in hematogenous dissemination and which might represent possible prognostic biomarkers.

PTs, CTCs, LNs and lungs were collected from the breast cancer (BC) MDA MB 231 xenograft model and characterized in two independent experiments using a microarray platform. CTCs were distinguishable from solid lesions by a set of 474 significantly differentially expressed genes. Among genes up-regulated in CTCs, the trefoil factor 3 secreted peptide (TFF3) was selected to evaluate its role in CTC biology. TFF3 down-modulation or knock-out (KO) significantly impaired MDA MB 231 cell migratory and invasive properties, but not their proliferation rate or vascular mimicry ability, in in vitro assays. Xenograft experiments with MDA MB 231 TFF3KO clones did not allow drawing conclusions on the involvement of TFF3 in dissemination and metastasis as the interpretation of results was hampered by the biological heterogeneity observed among clones. Interestingly, the expression status of TFF3 and some other CTC/metastasis-specific genes assessed in CTCs isolated from peripheral blood of BC patients, but not CTC status alone defined using standard markers, allowed identifying a group at higher risk of relapse or progression. Indeed, patients with TFF3+ CTCs had a significantly shorter progression-free survival compared to those with TFF3- CTCs. On the contrary, TFF3 expression level assessed in publicly available primary BC datasets did not correlate with tumor relapse.

The study of biologically relevant CTC-specific genes may allow deciphering the molecular mechanisms which orchestrate dissemination and real-time monitoring tumor evolution.