Background <p>Circulating tumour cells (CTCs) are mediators of cancer dissemination and the formation of metastasis, which is the leading cause of cancer-related deaths. Experimental models derived from CTCs contribute to understanding the biology of CTCs, their role in dissemination, and the discovery of potential drugs targeting CTCs.</p> Methods <p>A xenograft was derived from CTCs isolated from a patient diagnosed with metastatic invasive ductal carcinoma of the breast. The characterisation of the CTCs-derived xenograft (CDX) was conducted through in vivo experimental metastatic assays, RNA-Seq, spectral flow cytometry, and drug sensitivity tests.</p> Results <p>The CTCs-enriched fraction formed a CDX within 6 months, and its metastatic potential was confirmed. CDX cells were propagated in vitro, where the enrichment of CD44⁺/CD24⁻ breast cancer stem cells was confirmed. An RNA-Seq-based comparison of CDX with the primary tumour from the same patient unravelled substantial changes in genes related to cell growth, metabolism, and extracellular signalling. CDX and in vitro cell culture showed sensitivity to carboplatin. A partial response was also observed for vandetanib, which was selected through in silico analysis of transcriptomic data.</p> Conclusions <p>We present and characterise a novel model derived from CTCs for understanding the plasticity and behaviour of CTCs and advanced breast cancer.</p> <p></p>