CEA will be elevated in colon cancer and also in other conditions, but for mother it is a caution because of previous history. After 1 year completed treatment a colonoscopy is recommended. Get an colonoscopy done. If it’s fine but still CEA elevated then imagining is required.

CEA can rise due inflammatory causes also so may not be always a recurrence , endoscopy (colonoscopy) should be performed to rule out any local recurrence if it is indicated based on the patient’s post surgical status , that can also help us rule out any other cause of rise in CEA and can take biopsy from suspicious site . If that too is negative - keep on follow up and continue three monthly CEA ,6 monthly imaging (CE CT abdomen and pelvis) will be enough , no need of PET CT until it’s indicated. Since PET has been done now , no other imaging is required now . Endoscopy should be considered as mentioned above . If no imaging is done , consider colonoscopy followed by can consider CE CT scan , or PET CT . Every time when CEA value increases it’s better to get investigated as we have to rule out a recurrence. For any further advise please share your post operative reports and initial imaging as well as LAST PET CT report .