MCAM and neoplasm: So, transient CMCs expressing MCAM/MUC18, either if related to the tumour burden or spread after the surgical excision, should be interpreted as limited survival of early micro-metastases with short half-life and consequent absence of clinical proliferating activity, while a persisting or later achieved MCAM/MUC18 detection could indicate a mature metastatic proliferative behaviour, able to extravasate into the surrounding tissue by degrading basement membrane and extracellular matrix [25, 30, 45].