A randomized controlled trial comparing conventional ESD versus ESD with countertraction for early colon tumor

INTERVENTION: A:Conventional ESD group B:ESD with countertraction method group CONDITION: early colon tumor PRIMARY OUTCOME: ESD procedure time SECONDARY OUTCOME: 1,2,3)ESD procedure time according to the location of the lesion, Macroscopic type, traction type; 4) the rate of conversion case from conventional ESD to counter‐traction ESD; 5,6,7) procedure time of hemostasis; times of hemostasis; total quantity of injected solutions into the submucosa; 8)damage of specimen caused by counter‐traction; 9)en bloc resection rate; 10)complete en bloc resection rate; 11) serious adverse events; 12) the rate of snaring or Hybrid ESD due to difficulty of ESD INCLUSION CRITERIA: