That's what a tumor is, an unmannerly guest. Their pursuit of freedom inevitably encroaches on yours. Their swinging fist inevitably finds your nose. Tumors are incredibly American. They are you, and yet they are not you.
Normal cells have a purposeful DNA map.
Tumor cells are cells that have lost the map. They replicate not as brain but as callus. It is stupid as meat, but it edges out the pulsing angel that is your mind. Consider what the human brain is, in the context of all nature. It is the only instance we know of in the universe of atoms and molecules organizing themselves to think and speak.