Like I said, the only difference between benign and malignant is the growth rate. If you are going to die of old age before a cancer becomes a problem it is benign. If you double or triple estimated life expectancies, a lot of 'benign' tumors suddenly become malignant : )
I know that you know this stuff and you may even be technically correct depending on the definitions. I would call it accurate, but not true. How is that for a compromise?
In reality, its the capability to transfer growth factors to non-tumor cells ajacent to the tumor that is the difference. That is most of the reason for the irregular shape of malignant tumors.