TGFB1 and cancer: Of interest is the close association between platelets and CTC clusters because of the platelets’ ability to release TGF-β1 (Transforming Growth Factor Beta 1) – a signalling molecule that, in addition to its complex roles in normal activities (e.g., platelet-derived TGF-β1 functions in wound healing [41]), also plays a major role in many aspects of human cancers [42].