Songun 2010.

Methods	Method of randomization: "The sequence of randomisation was in blocks of six with stratification according to the participating centre." Exclusion after randomization: D1 = 133 (metastatic disease); D2 = 152 (metastatic disease) Lost to follow‐up: one Method of allocation concealment: "The sequence of randomisation was in blocks of six with stratification according to the participating centre." Intention‐to‐treat analysis: yes Description of sample size calculation: reported (expected number: 1062)
Participants	Number randomly assigned: 523 (D2 = 483, D1 = 513) Age < 70 years: 33% Sex (M/F): 401/310 Inclusion criteria: patients with resectable primary non‐metastatic gastric carcinoma Equivalence of baseline characteristics: age, sex and stage distribution similar for both groups
Interventions	D2 versus D1 lymphadenectomy (during gastrectomy)
Outcomes	Overall survival (D2 vs D1): HR 0.92, 95% CI 0.78 to 1.09 Disease specific survival (D2 vs D1): HR 0.74, 95% CI 0.59 to 0.93 Disease free survival (D2 vs D1): HR 0.95, 95% CI 0.82 to 1.10 Postoperative deaths: 32 (D2), 15 (D1)
Notes	Country: Netherlands Median follow‐up: 15.2 years
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk
Allocation concealment (selection bias)	Low risk
Blinding of participants and personnel (performance bias) All outcomes	Low risk
Blinding of outcome assessment (detection bias) All outcomes	Low risk
Incomplete outcome data (attrition bias) All outcomes	Low risk
Selective reporting (reporting bias)	Low risk
Other bias	Unclear risk	It is unclear whether the number of patients excluded after randomization had any impact on the trial outcomes.