The human body is obviously not a mouse - we obviously have size...

The human body is obviously not a mouse - we obviously have size differences by multiples - imagine the poor mouse having a suppository! I get the human tumour but this can be grown in the lab why put them in a mouse - how is that relevant to a human? if the compound attacks the tumour in a test tube then what is the point of putting that tumour into a mouse who is then given the compound/s?
I guess safety wise its a good idea to test it on a poor mouse before using it on a human but the human tumour is still a human tumour - it came from a human (presumably), putting it into a mouse with the differences in anatomy and physiology and diet and environment and DNA etc etc etc I would think is not a great indicator of how it would behave in a human - safety yes no argument. (having said that sometimes this is not the case in that what doesn't hurt a mouse can sometimes hurt a human as described in the below article)

Why Drugs Tested in Mice Fail in Human Clinical Trials

https://sitn.hms.harvard.edu/flash/2020/why-drugs-tested-in-mice-fail-in-human-clinical-trials/