A CTC Model Uncovers Metastatic Drivers and Prognostic Markers in Breast Cancer

Background: Circulating tumor cells (CTCs) and CTC-clusters are pivotal in the metastatic process of breast cancer (BC). Owing to their low frequency, models replicating their biology should provide a robust platform for investigating the molecular mechanisms driving metastasis and identifying new biomarkers. We established and characterized a CTC-derived cell model from a mouse xenograft to explore its metastatic behavior and molecular profile, which allowed us to investigate the expression and prognostic significance of a set of genes associated with the metastatic potential of CTCs. Methods: The CTC line (mCTC) derived from a MDA-MB-231 mouse xenografts was used in comparative functional analyses including cell cycle evaluation, colony formation, invasion, adhesion, and metastatic competency in zebrafish models. Transcriptomic profiling and functional assays were conducted to identify candidate genes and understand their roles in metastasis. Moreover, publicly available gene expression datasets of CTCs, CTC-clusters, and tumor tissue, from GEO and TCGA, were analyzed for the identification of a gene signature that was correlated with survival data. The signature was validated in an independent cohort. Results: Compared with MDA-MB-231 cells, mCTC cells presented enhanced colony formation, invasion, and adhesion, and increased dissemination and survival in zebrafish. Transcriptomic analysis revealed that SPARC was significantly upregulated. Functional assays showed that SPARC overexpression was correlated with increased invasion and migration. Analysis of public datasets confirmed the high expression of SPARC in BC CTCs and CTC-clusters. Additionally, a 4-gene signature involving SPARC, THBS1, VCL, and HSP90AB1 was identified that demonstrated strong prognostic value, predicting shorter overall and distant metastasis-free survival in the primary tumor setting. Validation cohorts confirmed its ability to distinguish high-risk patients. Elevated expression of the 4-gene signature in CTCs was also indicative of increased mortality risk. Conclusion: mCTC exhibit distinct metastatic traits and molecular characteristics, highlighting a possible role of SPARC in CTC biology and its potential as a prognostic marker in BC metastasis. The identified 4-gene signature provides a robust prognostic tool for assessing patient risk and guiding therapeutic strategies. Further investigations into the mechanistic role of SPARC may reveal new therapeutic targets for managing BC progression.