Uterine Adenocarcinoma - Rabbit
Introduction
This is the most common neoplasm in rabbits, with an incidence of up to 60% in intact females over 3 years old.
The tumour arises from the endometrial glandular epithelium. It may be preceeded by endometriosis, endometritis, endometrial hyperplasia or endometrial venous aneurysms. These tumours frequently bleed and the haemorrhage can be life-threatening.
The tumours metastasise locally by extension into the myometrium and peritoneum, but also to distant locations such as the lungs, brain, bone and liver.
Tumours are usually present in both uterine horns and may occur simultaneously with pyometra or pregnancy.
Mammary neoplasia or cystic mastitis are often found in does with uterine adenocarcinoma.
The disease occurs in intact females over the age of 3-4. All breeds are at risk but the highest incidence is reported in French Silver, Havana and Dutch breed does.
Clinical Signs
Does are usually presented for haematuria by the owner. It isn't true haematuria, but blood is released from the uterus during micturition. Blood clots are sometimes seen.
There may also be a serosanguinous vaginal discharge.
Cystic mastitis or neoplasia may involve one of more mammary glands.
If does are presented late in the disease with metastasis, they may show signs of lethary, dyspnoea and pale mucous membranes.
The tumour may not be palpable until late in the disease process, but may feel as firm midcaudal masses palpable between the bladder and colon.
Diagnosis
Haematology and biochemistry will determine the overall health status of the animal, and may reveal a variably regenerative anaemia. There may be increased liver enzymes with metastasis.
Abdominal radiography may reveal an abdominal mass, dorsal to the bladder
Thoracic radiography may reveal evidence of metastases.
Ultrasonography is very useful in outlining the location and architecture of the uterine mass.
An ultrasound-guided cystocentesis can be performed to differentiate between haematuria and uterine bleeding.
Mammary masses can be examined with cytology.
Histopathology is required for a definitive diagnosis, and will reveal a well-differentiated adenocarcinoma
Gross inspection of the uterus shows: cauliflower-like or papillary projections into the uterine lumen. The tumours may be multicentric involving both horns, and may have a haemorrhagic or necrotic centre.
Differential Diagnoses
Endometrial venous aneurisms
Pregnancy
Endometrial hyperplasia, hydrometra or mucometra
Pyometra
Other uterine tumours
Other mid-caudal abdominal masses
Treatment
Ovariohysterectomy is the treatment of choice, and is curative if metastasis has not occurred.
Even if metastasis is not grossly visible at the time of surgery, checks should be performed at 6-monthly intervals and a the prognosis is still guarded.
Good nursing care is paramount in ensuring rabbits do not develop ileus and other gastro-intestinal problems post-operatively.
A blood transfusion may be necessary if the rabbit is severely anaemic or there is significant haemorrhage during surgery.
Neoplastic mammary glands should also be excised.
If metastasis is evident on radiographs, the prognosis is grave and euthanasia is the best option.
Prevention
Ovariohysterectomy is recommended for all non-breeding rabbits, usually between 6 months and 2 years of age.
If rabbits are used for breeding, this should be stopped at 4 years and rabbits spayed, as this is when most tumours occur.
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References
Rosenthal, K. (2008) Rapid review of exotic animal medicine and husbandry Manson Publishing
Oglesbee, B. (2006) The 5-minute veterinary consult: ferret and rabbit Wiley-Blackwell
Merck and co (2008) The Merck Veterinary Manual Merial