CD274 and ovarian carcinoma: The results of meta-analysis demonstrated that PD-L1 expression was not correlated with tumor grade (OR = 1.63, 95% CI = 0.90–2.96, P = 0.109, n = three studies with 640 ovarian cancer patients) and clinical stage (OR = 1.14, 95% CI = 0.68–1.91, P = 0.607, n = nine studies with 1326 patients with ovarian cancer) (Fig. 2).