Celecoxib, an inhibitor of cyclooxygenase 2 (COX2), and nelfinavir, an HIV protease inhibitor, both induce ER stress by causing leakage of calcium from the ER into the cytosol via the induction of ROS in colorectal cancer, myeloma, and prostate cancer as well as HPV-transformed cervical carcinoma, head and neck cancer, pancreatic cancer, and melanoma [45,46]. Here, PTGS2 is linked to head and neck cancer.