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| Author | Year | No. | Study design | Tumor location (%) |
|---|---|---|---|---|
| Jeon et al.40 | 2018 | 275 | Single center | Upper (4.4) |
| Middle (33.1) | ||||
| Lower (62.5) | ||||
| Kim et al.3 | 2015 | 292 | Single center | Upper (7.2) |
| Middle (14.4) | ||||
| Lower (78.4) | ||||
| Ryu et al.41 | 2016 | 144 | Multicenter | Upper (4.9) |
| Middle (32.9) | ||||
| Lower (62.2) | ||||
| Hahn et al.42 | 2018 | 1,206 | Multicenter | Upper (8.3) |
| Middle (32.8) | ||||
| Lower (58.9) |
