Cancer: Not all brain tumors are made the same, and that’s important
When you look at an apple, no matter what variety, on the surface you can be pretty sure it's actually an apple. From there, you can make lots of assumptions about it, like how it will taste when you bite into it and what will happen if you plant the seeds in your yard.
With cancer, we can't make those kinds of assumptions. While two tumors from the same location in two patients may look the same, doctors and researchers have come to recognize that their behavior and the mutations driving them can be radically different, as can their response to therapy.