Surgery is often the best treatment for colon cancer. However, chemotherapy is also administered to minimize the risk of recurrence. Recent clinical findings demonstrate that many patients who undergo surgery for colon cancer do not need any chemotherapy.
Moreover, advances in therapeutics and patient care have reduced the recurrence risk which in turn decrease the chances of giving chemotherapy and associated harmful adverse effects. Source: Erik Osterman et al. Recurrence Risk After Up-to-Date Colon Cancer Staging, Surgery, and Pathology, Diseases of the Colon & Rectum (2018)
