Regarding uterine cancer in female rabbits, a quick run to _The Biology of the Laboratory Rabbit, 1994 edition_ (TBLR) pops up the following information. Adenocarcinoma of the uterus is the most frequently encountered neoplasm of the rabbit. Ingalls (J. Natl. Cancer Inst. 33:799-806. 1964) showed that 11 of 12 rabbits developed uterine carcinoma. Because of the number of rabbits developing carcinoma many researchers looked into the possibility of estrogen being carcinogenic (because of the high levels of estrogen constantly in a mature rabbit's system). There was quite a bit of conflicting data, and the authors draw this conclusion "Data is extremely difficult to interpret because of the naturally high incidence of adenocarcinoma of the uterus in untreated rabbits."
Later the reviewer writes, "Notwithstanding heredity as a factor, the incidence of uterine carcinoma has been noted to exceed 50% in certain colonies of random bred females kept past 5-6 years."
Perhaps the best article (and probably where everyone gets the 80% figure that's been quoted over and over) was publised by Green in 1958 (Ann NY Acad. Sci. 75:535-542). Greene monitored a colony of rabbits over a long period of time (8-10 years, I think). All rabbits dying from whatever causes were necropsied. 16.7% of 849 rabbits were found to have uterine adenocarcinoma. The average age of the colony was greater than 4 years, which is important, because most lab rabbits are under 24 months of age. A very important finding was tight correlation between tumor incidence and age in Greene's colony. In rabbits dying between 2 and 3 years of age the incidence of cancer was 4.2%. In rabbits 5-6 years of age the incidence is 79.1% (the mythical 80%). Note: these rabbits did not necessarily DIE from the cancer, but there were tumors found in the uterus during necropsy. I don't know what the different causes of death were, but they are listed as "natural". The incidence of cancer in males and females is about the same in rabbits under two years of age, after that, the incidence in females dramatically increases over the males, primarily due to uterine cancer.
From talking with various vets and animal health people, it seems that some people don't believe cancer is a problem and others do. I happen to be one that believes it. I found the article in _TBLR_ because it was referenced in a journal article discussing cancer in rabbits which claimed that the incidence of cancer was somewhere between 1 and 4% in rabbits (I don't remember the exact figure). Not believing it, I checked. That low figure was compiled from laboratory rabbits, most under 2 years of age. However, that figure agrees very well with Greene's findings, that there is a very low incidence of cancer in young rabbits. When one starts looking at older rabbits the data drastically changes. Most of the vets I've talked to seem to believe that this is a genetically controlled trait. _TBLR_ even lists breeds that are not susceptible to uterine cancer (A list I hesitate to reproduce because I'm not sure how true it is). While 80% may not be a figure for the rabbit population in general, it was for that colony, composed of genetically diverse animals. Other people have reported colonies with a >50% incidence of cancer.
The threat is real, and is acknowledged by the veterinary and scientific community who have worked with rabbits, particularly older rabbits. I've talked to vets who say it's not, but all of the veterinarians who I would trust to touch my animals do view it as a real risk.
