To evaluate this hypothesis, CT26-bearing mice (tumor size 227 ± 14 mm3 on day 10) treated with ICIs (anti-PD-1 or anti-CTLA-4 antibody), class I HDAC inhibitors (chidamide or mocetinostat), and COX-1/COX-2 inhibitors (celecoxib, aspirin, or ibuprofen) were evaluated. The gene discussed is HDAC9; the disease is neoplasm.