CD9 and cancer: The pooled results remained unchanged, indicating a significant association between CD9 expression, OS, and DFS in cancer patients (for OS, HR 0.47, 95% CI 0.31–0.73, p = 0.001; for DFS, HR 0.48, 95% CI 0.30–0.79, p = 0.003) (Fig. 6C–D).