Waiting time for therapy

Perfectly reasonable question. The tumour has gone but cancer cells can spread, often through lymph nodes, and may still be capable of developing. Chemo is recommended to kill off fast growing cells (unfortunately that often means your hair too!) which may well be cancerous or potentially cancerous. Research is looking for ways to hone in more accurately on the rogue cells but until that is better developed, we use a sweeper approach (kill off anything that mighty be...). It’s not absolutely guaranteed but in many cases it still seems to be most effective course of action.