It can be found here.
The upshot of it seems to be that the longer your rabbit lives, the more prone it is to get uterine cancer. Oh...big surprise that. That's the way it is in any population of animals. Older animals are more prone to get diseases. The older animals get the more likely you are to get cancers.
Now..that said. Rabbits can live 10 years+ of age if well cared for. So you may wish to consider doing neutering if you are a pet owner. Do Note though, spaying does NOT completely remove the possibility of your rabbit getting uterine cancer. I've known of at one case - from a pet rabbit owner wanting a rabbit to replace the SPAYED rabbit she had that developed uterine cancer. And I've heard via rabbit boards of similar situations.
If you are a breeder, you probably won't have to deal with this issue. Your rabbits probably won't be around long enough. BUT if you have a favourite that you hold back, and if you notice blood in the urine... be alert to the possibility that your rabbit may have uterine cancer.