A Phase III Trial of Anus-preservation in Low Rectal Adenocarcinoma Based on MMR/MSI Status

3mg/Kg iv d1q2w

IMRT 50Gy/25fx 625mg/m2 bid d1-5 qw Irinotecan:1、Full wild (GG+6/6): 80mg/m2/week for 5 times 2、Single site mutation (GG+6/7 or GA+6/6): 65mg/m2/week for 5 times 3、Double locus mutation (GG+7/7 or AA+6/6 or GA+6/7): 50mg/m2/week for the 1st, 2nd, 4th and 5th week for 4 times

25Gy/5fx

Capecitabine: 1000mg/m2 bid d1-14 Irinotecan: 200mg/m2 ivgtt d1 q3w

Irinotecan: 150mg/m2 ivgtt d1 (double locus mutation downregulated to 120mg/m2) Oxaliplatin: 85mg/m2 ivgtt d1 5-FU: 2400mg/m2 ivgtt 46h q2w