PTGS2 and neoplasm: Cyclooxygenase 2 (COX2) expression in human tumours has been linked to radioresistance, while its inhibition was shown preclinically to increase tumour radiosensitivity through different MOA, including angiogenesis suppression and apoptosis induction (figure 3).37–41 These findings led to the clinical testing of celecoxib, a selective COX-2 inhibitor used as analgesia, concurrently with RT/CRT.