CASP9 and head and neck squamous cell carcinoma: Moreover, mutated p53 is involved in the resistance to chemotherapy in head and neck squamous cell carcinoma (HNSC) through the inhibition of the p73 pro-apoptotic transcriptional program [123], or the blocking of caspase 9 activity [124] and caspase 9-mediated activation of mitochondrial caspase 3 [125].