The majority of the risks of treatment for colon cancer are associated with side effects of the medications.  I will say that the risk of NOT treating colon cancer is higher than any of them.  The main risks of surgery for colon cancer are bleeding and infection.  There will likely be some degree of pain or discomfort afterwards as well.  These things we can control with medication.  If you require an ostomy bag after the operation there may be skin irritation and pain associated with that as well.  If radiation is required for the colon cancer, it can cause radiation damage to the tissues and organs around the colon.  This can cause scar tissue to develop which may lead to abdominal pain and it can cause radiation damage to the tissues that can result in bleeding later on.  If you require chemotherapy there are many different side effects depending on which chemotherapy you get.  Most common problems with chemotherapy are increased risk of infection, nausea and vomiting, diarrhea, hair loss and fatigue.  We have medications available to help lessen most of those symptoms but sometimes they get bad enough that the chemotherapy has to be stopped.