Uterine Cancer in the Doe

By Linda Dykes MBBS (Hons) and Owen Davie BVSc MRCVS

The vast majority of female rabbits will develop cancer of the uterus (womb) in middle age. Shocking figures, but the facts aren't new - the studies were published nearly 40 years ago. Vets and rabbit experts didn't really take the information on board: there was very little anyone could do about it until improvements in rabbit anaesthesia over the past few years made routine spaying a reality.

From an evolutionary perspective, rabbits are not designed for longevity. Wild rabbits are old at two and only a fraction pass four years of age: wild female rabbits die long before uterine cancer develops and hence the disease is not a survival disadvantage to the species. It's not known exactly why the uterus of a female rabbit is programmed to self-destruct. Presumably it's the penalty paid for high levels of circulating hormones earlier in reproductive life and the way uterine tissue responds to these hormones.

What we do know is that uterine cancer is the commonest cancer of rabbits and is the end point of a gradual process becoming much more common with increasing age. The classic study (Greene, 1958) which is so widely quoted in houserabbit circles showed 4% of does had uterine cancer age 2-3 years of age, rising to 80% at 5-6 years. It doesn't make any difference whether the doe has been bred from or not (Adams, 1962) or what breed she is.

Breeding does who develop uterine cancer invariably have a history of reproductive disturbance in the 6-10 months prior to the tumour becoming detectable by palpation. Typical problems are reduced litter size, stillborn litters, and does deserting their litters. Dystocia (difficulty kindling), litter retention in utero, abdominal pregnancy and fetal resorption are also more likely when tumours are developing. The tumours are usually multiple and the growth rate varies widely. Some tumours grow large rapidly; others remain small but throw off metastases and spread to other parts of the body such as the lungs. The time from detection of the tumour to death from metastases ranges from 12 to 24 months.

These are the facts. The next question is how to tackle the problems posed by this common and deadly disease?

• Female rabbits not required for breeding should be spayed. The uterus and both ovaries are removed in a spay operation which effectively prevents uterine cancer so long as every remnant of uterine tissue is removed.
• Rabbits with early uterine tumours may be saved if they are spayed when the cancer is still contained within the uterus, before metastasis has occurred. Blood in the urine is sometimes an early sign of uterine cancer and should be taken seriously in female rabbits.
• Anyone planning to retire a breeding doe as a pet should be alert to any changes in reproductive behaviour which may indicate uterine problems. Arrangements can then be made for the doe to be spayed promptly and either kept or rehomed as a pet.
• Most rabbit owners have no idea that their doe likely to die prematurely if left unspayed. If rabbit fanciers take the opportunity to educate people buying a female rabbit as a pet (be it hutch rabbit or houserabbit) then the new owners can make an informed decision whether or not to have the doe spayed. Although the operation itself carries a degree of risk, it confers multiple benefits by preventing cancer, decreasing aggression, facilitating housetraining in the indoor rabbit and permitting multiple rabbits to be kept together in a more natural social system than solitary confinement.

References

Greene, HSN 1958 Adenocarcinoma of the uterine fundus in aged rabbits. Am J. Pathol. 68: 653-56

Adams, WM Jr 1962 The natural history of adenocarcinoma of the uterus in the Phipps rabbit colony. N. Med. Sci Thesis, Henry Phipps Institute, Univ of Pennsylvania, Philadelphia.

Percy, DH and Barthold, SW Pathology of laboratory rodents and rabbits Iowa State University Press 1993, pp 222-224

Manning, PJ; Ringler, DH; Newcomer Christian, P The Biology of the Laboratory Rabbit pp 262-266 2nd edition 1994 San Diego Academic Press.

Many thanks to Sally Walshaw MA, VMD (American veterinary advisor to the British Houserabbit Association) who kindly conducted the literature search necessary to compile this article.