In stratified analysis by tumor site (Additional file 1: Tables S6 and S7), eight (STXBP6, CSAG1, CD86, POLR2F, CLSTN3, ADPGK, CSF2RA, CHRDL2) of the 13 proteins were associated with colon cancer risk using Wald ratio or IVW method, and two (CHRDL2, CD86) were associated with rectal cancer risk (P < 0.05). Here, CSAG1 is linked to malignant colon neoplasm.