I Had A Colonoscopy 5 Days Ago. At That Time

I had a colonoscopy 5 days ago. At that time my doctor told me that he found a tumor, so he did a biopsy. Today he called to say that the results are that it is pre-cancerous. I have an appointment to talk to him in a week. My question to you is, why did he not remove the tumor while he was in there instead of just a biopsy. What does a pre cancerous diagnonsis mean and what is envolved? I am a 68 year old female with no family history of colon problems.