SMAD2 and head and neck squamous cell carcinoma: As reported in a previous study evaluating TGF-β signalling between marginal and central areas within tumour tissue,27 the expression levels of p-SMAD2 were significantly higher in tumour cells located at marginal tumour areas than those at central tumour areas (Fig. 3c), indicating that HNSCC cells located at marginal tumour areas showed more response to TGF-β1 stimulation than central areas.