The results showed no significant correlation between COX‐2 expression and cancer histology (nine studies with 371 cases: osteogenic osteosarcoma vs. nonosteogenic osteosarcoma: OR = 0.87, 95% CI = 0.52–1.45, P = 0.583) (Fig. 11) or necrosis (four studies with 163 cases: ≥ 90% vs. < 90%: OR = 1.39, 95% CI = 0.54–3.56, P = 0.491) (Fig. 11). The gene discussed is PTGS2; the disease is cancer.