You have mentioned it was an ascending Colon carcinoma in 2024. After treatment, the present active disease on MRI is in the rectosigmoid location with wall thickening. And the present sigmoidoscopy shows normal anastomosis is mentioned. The anastomosis for a surgery for an ascending colon cancer surgery would not be seen in the left colon in sigmoidoscopy. In that case, maybe a full colonoscopy has already been done now (?). These points you can clear with your doctor there and please update. The present lesion seen on MRI is a new primary. It’s in a different part of colon. Will need to do a PETCT or Contrast CT of neck thorax and abdomen to look for other metastases. Need to do a biopsy from this rectal wall thickening or an accessible metastatic lesion. Need to do MMR IHC on the biopsy and selected NGS panel if possible. Based on the present MRI, it has advanced locally with infiltration of surrounding tissues and nearby nodes. Can plan further therapy based on the final staging and the molecular reports. Also can do a PSA and CEA

You need to do a complete colonoscopy and rule out any recurrent lesions and if normal can be on regular follow up