EPCAM and head and neck squamous cell carcinoma: Considering that EpCAM positivity in primary HNSCCs is correlated with good prognosis and epithelial differentiation [27], it is conceivable that isolated HNSCC‐DTCs tend to be EpCAM‐low or EpCAM‐negative, for example, triggered by epithelial‐to‐mesenchymal transition (EMT) [28].