Circulating tumor cell (CTC)

A circulating tumor cell (CTC) is a **cancer cell** that has detached from a primary tumor and entered the bloodstream (or, less commonly, the lymphatic system)[4][7][9]. CTCs play a key role in the metastatic cascade by enabling the spread of cancer to distant organs. While the majority of CTCs perish in circulation due to shear stress, immune surveillance, or anoikis, a small subset survives, extravasates, and potentially initiates metastatic tumors[7][4][1]. CTCs exhibit considerable **heterogeneity**, including cells undergoing epithelial-to-mesenchymal transition (EMT), and may form multicellular clusters (CTC clusters or microemboli) with enhanced metastatic potential and therapy resistance[4][7]. While CTCs inform on **cancer biology** and are important as **biomarkers for prognosis, treatment response, and disease progression**, they are not single molecular targets but rather a diverse, dynamic population of cells[8][2][5]. Various surface markers (e.g., EpCAM, PD-L1, vimentin) help in their detection and characterization, which guides therapy selection and patient monitoring[2][5]. Because "Circulating tumor cell" refers to a heterogeneous population of cells and not a discrete molecular entity or receptor, it is not considered a direct therapeutic target in the conventional sense (such as an enzyme or receptor)[7][9]. Research is ongoing to exploit CTCs for therapy or as surrogates for therapy selection, but at present, interventions target surface markers or characteristics rather than CTCs as a standalone target[5][7]. Key points on why this entry is marked as incorrect: - "Circulating tumor cell" is *not* a discrete molecular entity, receptor, enzyme, or protein, but a **cellular population** with varied origin and phenotype[7][4]. - The entry should instead specify a molecular marker on CTCs (e.g., EpCAM, PD-L1) if seeking a druggable target[2][5]. - No therapies directly target "circulating tumor cells" as such, but some aim at surface antigens or use CTC count as a biomarker[5][2]. - It is not appropriate to treat "circulating tumor cell" as a canonical drug target per standard molecular oncology conventions.

Other names

Circulating tumour cellCTCCirculating cancer cell