The first pMMR/MSS tumor was in the ascending colon and was RAS-RAF-wildtype with alterations in TP53, CTNNB1, and a tumor mutational burden (TMB) of 6.4 Mut/Mb, whereas the second tumor was a rectal cancer above the peritoneal reflection (candidate for upfront surgery), KRAS-G12V mutant, and with truncating alterations in APC gene and a TMB of 4.7. This evidence concerns the gene CTNNB1 and rectal cancer.