PTGS2 and osteosarcoma: The results showed that COX‐2 expression was not associated with age (two studies with 81 cases: ≥ 20 years vs. ≤ 20 years), gender (seven studies with 252 cases: male vs. female), or tumor location (two studies with 66 cases: femur vs. nonfemur) of osteosarcoma (OR = 0.56, 95% CI = 0.09–3.49, P = 0.534; OR = 1.05, 95% CI = 0.47–2.37, P = 0.903; OR = 1.06, 95% CI = 0.26–4.41, P = 0.933, respectively) (Fig. 10).