RAC1 and head and neck squamous cell carcinoma: Of the several possible molecular mechanisms in EMT progression, Twist1 has been identified as a master regulator of morphogenesis which plays an essential role in tumour metastasis.30, 31 We previously reported that Twist1 cooperates with BMI1 to suppress the expression of microRNA let‐7i, resulting in the activation of Rac1 and inducing mesenchymal movement in 3D environment.31 In this study, we observed that, in 3D culture environment, Rac1 activation of mesenchymal‐like HNSCC cells (SAS & OECM‐1) were significantly higher than that of epithelial‐type cells (FaDu & CAL27) (Figure S2).