All Cancer Was Removed At My Surgery. Why Do I Need Additional Treatment?

this is an image of a woman confused. It is used as a featured image to represent the questions after cancer surgery that patients have regarding need for further treatment. For an article by Dr Suraj Manjunath, best cancer surgeon/surgical oncologist, Bangalore

Common questions following surgery for cancer are:
If the cancer was completely removed, why do I need more treatment?
Chemotherapy and radiotherapy have side effects, and will take so much time – are they really necessary?
What if I opt not to take any further treatment?
This article discusses the concept of adjuvant treatment and why some people require it.