I am going to inject mice tumour cells into mice to create them tumours and I am wondering if I need to have special precautions for that, even they are cells from mice tumour I am afraid what can happen if I inject myself by accident, I guess is not necessary to do it a hood either?
You should not be asking random people on the internet about this. Talk to your lab safety people. Get detailed instructions on handling requirements. As for the hood, again, do not ask here, ask your animal care people (IACUC or equivalent). If you don't have both lab safety people and animal care people immediately available and involved before the experiment begins, you should not be doing this experiment.