I will freely admit that I just read Veks' synopsis and did not click on the article; perhaps it answers this question.
However, I confess to being a little confused. There are a lot of cells with anti-crowding genetics; it's the reason your liver is not the largest organ in your body, for instance, or why your kidneys are not the size of your head. One of the basic traits of the genetic mutations that cause tumors (and cancer) is the disabling of the natural claustrophobia that cells have.
This is not news. This is taught in genetics classes across the country.
So I'm wondering why the discovery that these rats have such a common genetic trait is ... news. It's good that those genes resist the mutations more robustly than other sets of genes, but when you get right down to it, cancer is a huge series of mutations that involves the disabling of failsafes and the enabling of certain unhealthy behavior in ... a single cell. It just takes one cell.
Edit: I should probably make it clear that I'm not exactly pro-cancer or something crazy. Yay, breakthrough, etc - but I dislike being patronized and patted on the head by being shown a new version of old news.