2 Answers

benign sorta stays in place malignant is aggressive and spreading

matheneyg is correct. To put it simply, benign means non threatening. It just sits there and grows in one place. Normally, it can be removed or irradiated in place and is, if you have to have either, the one to have. The malignant is the one which grows, spreads, and hides in other places, making it as difficult to kill as a dandelion with a really good root system. In order to get rid of the malignant tumor, doctors are normally much more aggressive, taking more tissue, using chemo in addition to radiation, and also using surgical techniques when called for. Its like having a bad case of root worm in a farmer's corn field - have to treat the entire field, the neighbors fields too, if you want to make sure they don't resurface somewhere else.