Table 1 The quality and characteristics of included studies
| Study | Randomization |
Allocated Concealment | Blinding | Gemcitabine (sample size) | Mitomycin (sample size) | Grade |
|---|---|---|---|---|---|---|
| Dong 2017 [16] | adequate | not used | clear | 12 | 16 | C |
| Lin 2016 [17] | adequate | not used | clear | 42 | 42 | C |
| Sun 2016 [18] | adequate | used | clear | 30 | 28 | B |
| Xiaohong 2015 [19] | adequate | not used | clear | 27 | 29 | C |
| Raffaele 2010 [20] | adequate | used | clear | 54 | 55 | B |