PTGS2 and colorectal cancer: To determine whether inhibition of COX-2 enzyme activity is a promising approach for sensitizing colorectal cancer cells to cetuximab, we examined whether treatment of DiFi5 cells with one of the COX-2 inhibitors used in Figure 1E could achieve an enhanced therapeutic effect through induction of apoptosis in cetuximab-resistant colorectal cancer cells when used in combination with cetuximab.