Rabbit Uterine Adenocarcinoma: Signalment, Staging, and the Ovariohysterectomy Decision

Bottom line

Uterine adenocarcinoma is by far the most common tumor of intact female rabbits, with reported incidence as high as 60% in does over three years of age [1]. It is a slow-growing endometrial carcinoma that often stays clinically silent until hematuria or a serosanguineous vaginal discharge appears, and ovariohysterectomy is curative when the tumor is still confined to the uterus [2]. Because hematogenous metastasis to the lungs, liver, brain, and bone follows within one to two years, the decision that changes the outcome is timing — spay electively before disease develops, or resect promptly once a uterine mass is found and thoracic metastasis has been excluded [2]. Prognosis is excellent after complete removal of pre-metastatic disease and grave once pulmonary spread is present.

Disease at a glance

• Entity. Endometrial adenocarcinoma arising from the uterine mucosa of the intact doe. Rabbits have a duplex uterus — two horns, two separate cervices, and no shared uterine body — so lesions are frequently bilateral and multicentric, and complete removal of both horns and both cervices is required.
• Signalment. Middle-aged to older intact does. In one clinical series the mean age at adenocarcinoma diagnosis was 6.1 years, versus 4.5 years for endometrial hyperplasia [5]; the tumor is uncommon before three years, with incidence climbing sharply in older does [1].
• Prevalence. The single most common neoplasm of the rabbit [1]. Classic research-colony data reported an overall incidence of 16.7% in does older than two years, varying widely with age, breed, and genetic constitution [4]. Modern hospital data agree that it is common: uterine disorders were found in 26.8% of 854 necropsied does, with adenocarcinoma the most frequent uterine tumor [6].
• Pathophysiology. A slow-growing carcinoma that commonly progresses from endometrial hyperplasia, extends locally into the myometrium and peritoneum, and only later disseminates hematogenously to the lungs, liver, brain, and bone [2].
• Key features. Hematuria or serosanguineous vaginal discharge [3], declining fertility [7], and concurrent cystic mastitis or mammary change [1]; late dyspnea from pulmonary metastasis is an ominous sign [7].

Signalment and age-related prevalence

Age is the dominant risk factor, and incidence climbs markedly in older intact does — reported as high as 60% in does over three years of age [1]. In a large series of 1,928 rabbits presented for ovariohysterectomy, 53.7% had endometrial adenocarcinoma and 43.7% had endometrial hyperplasia on histology, and the odds of adenocarcinoma rose with age at surgery (odds ratio 1.826) [3]. That 53.7% reflects a population selected for spay and is therefore enriched for disease; unselected necropsy data are lower, with uterine disorders in 26.8% of does and adenocarcinoma the most common uterine tumor [6]. Breed matters as well: the often-quoted figure that tan, French Silver, Havana, and Dutch does over four years of age reach a 50–80% incidence comes from older breeding-colony literature [2], and is best read against Greene's colony-wide figure of 16.7% [4]. The practical message is unchanged — treat any intact doe over three to four years as being at meaningful risk.

Clinical presentation

Early disease is frequently subclinical, passing through a hyperplastic endometrial stage before signs appear [2]. The first abnormality owners notice is usually hematuria or a serosanguineous vaginal discharge [2]; in the 1,928-doe series this was the presenting sign in 52.9%, the single most common clinical finding [3]. The blood is uterine in origin and is often most obvious at the end of urination, so it can be mistaken for lower-urinary hematuria. Reproductive failure — reduced fertility, smaller litters, and more stillbirths — commonly precedes a palpable tumor, in classic descriptions by 6 to 10 months [8]. Concurrent cystic mastitis or mammary enlargement is common, reflecting a shared hormonal drive [1]. Advanced disease brings anorexia, weight loss, abdominal distension, pale mucous membranes from chronic blood loss, and secondary gastrointestinal stasis [7]; dyspnea — from pulmonary metastasis or from sheer abdominal mass effect — is a late and grave development [7].

Diagnosis and staging

Physical examination often reveals a firm, sometimes multinodular caudal abdominal mass between the bladder and colon; Merck describes the lesions as globular polypoid structures on palpation [1]. Uterine nodules can be palpated or seen on abdominal radiographs and ultrasound or found at laparotomy, and the diagnosis is confirmed by histopathology [8]. Abdominal ultrasound characterizes the uterine mass and screens the liver, while three-view thoracic radiographs are the pivotal staging step: pulmonary metastasis is the finding that reclassifies a curable case as incurable, and should be obtained before any owner is told that surgery will be curative. Differentials for red urine or a caudal mass include endometrial hyperplasia, benign uterine lesions, normal urinary porphyrin pigment, and lower urinary tract disease such as cystitis or urolithiasis; a systemically ill older doe also warrants screening for comorbidities such as E. cuniculi.

Treatment: ovariohysterectomy

Complete ovariohysterectomy is the treatment of choice and is curative when the tumor is still contained within the uterus [2]. Because rabbits have two cervices and disease is frequently bilateral, both uterine horns and both cervices must be removed; residual uterine or cervical tissue risks recurrence. Stage before or during surgery — exclude pulmonary metastasis on thoracic radiographs, and inspect the liver, peritoneum, and regional nodes at laparotomy, remembering that microscopic metastasis or peritoneal invasion may not be macroscopically apparent [2].

Perioperative management, not the resection itself, is where rabbits are most often lost. Preserve body temperature, provide multimodal analgesia, and protect the gut. Opioids such as buprenorphine and NSAIDs such as meloxicam are used off-label in rabbits — dose them from Carpenter's Exotic Animal Formulary and see rabbit analgesia dosing — and anticipate post-operative ileus with early prokinetic support, fluids, and assist feeding. Because a chronically bleeding tumor can leave a patient anemic, check PCV and total protein before anesthesia.

Prognosis by metastatic status

Prognosis is bimodal and hinges entirely on metastatic status at surgery.

• Pre-metastatic, tumor confined to the uterus: ovariohysterectomy is curative and the prognosis is excellent [2].
• Local peritoneal invasion or occult spread: the prognosis is guarded even when the resection looks complete, because metastatic disease or peritoneal invasion may not be macroscopically apparent at laparotomy; follow-up examinations every three months for one to two years are warranted [2].
• Overt metastasis (pulmonary, hepatic, or other): the prognosis is grave. Hematogenous metastasis develops within one to two years of the tumor becoming detectable [2], and the classic interval from clinical detection to death — usually after metastasis — is 12 to 24 months [8]; pulmonary metastases were confirmed at euthanasia in several does in one clinical series [5].

The corollary is straightforward: outcome is decided by how early the uterus is removed, which is why thoracic screening and prompt surgery — not chemotherapy — are the levers that matter.

Prevention and spay timing

Elective ovariohysterectomy is the definitive preventive and is the primary reason to spay any non-breeding doe [1]. Merck recommends spaying non-breeding females at 4 to 6 months of age [1]; textbook guidance is to spay before two years of age, with 6 to 9 months preferred because younger does carry less intra-abdominal fat and are safer, more straightforward surgical candidates [2]. For does already past that window, spaying at diagnosis remains curative if performed before metastasis, so age alone is never a reason to withhold surgery from an otherwise healthy older doe [2]. Counsel owners of intact does on the early signs — any blood in the urine or vaginal discharge warrants prompt examination [7]. The same reproductive-disease burden drives elective spay recommendations across exotic companion species; for the analogous decision in another common exotic, see guinea pig ovarian cysts.

Frequently Asked Questions

At what age should I worry about uterine adenocarcinoma in an intact doe?

Risk rises sharply with age. Merck reports incidence as high as 60% in does over three years old, with the tumor uncommon before that age [1]. In practice, treat any intact doe over three to four years as being at meaningful risk, and raise the index of suspicion further in older animals, since the odds of adenocarcinoma increase with each additional year (odds ratio 1.826 in the largest series) [3].

Is ovariohysterectomy actually curative?

Yes, when the tumor is still confined to the uterus — complete ovariohysterectomy is curative in that setting [2]. The caveat is staging: microscopic metastasis or peritoneal invasion may not be visible at laparotomy, so a guarded prognosis and follow-up examinations are appropriate even after an apparently complete resection [2]. Rule out pulmonary metastasis with thoracic radiographs before promising a cure.

What is the most common presenting sign?

Hematuria or a serosanguineous vaginal discharge — this was the presenting complaint in 52.9% of rabbits in a series of 1,928 does, making it the single most common finding [3]. The blood is uterine, not urinary, and is often most obvious at the end of urination [2].

Do I need thoracic radiographs before surgery?

Yes. The lung is a principal metastatic site, and pulmonary metastasis is the finding that separates a curable case from an incurable one [2]. Pulmonary metastases have been confirmed at euthanasia in affected does [5], so three-view thoracic radiographs are a standard staging step before you counsel an owner on prognosis.

How common is uterine adenocarcinoma really — is the 50–80% figure accurate?

It depends heavily on the population. The 50–80% figures come from specific older breeding colonies (tan, French Silver, Havana, and Dutch does over four years) [2], while Greene's colony-wide incidence was 16.7% in does over two years [4]. In a spay-selected hospital population 53.7% had adenocarcinoma [3], whereas unselected necropsies show uterine disease in 26.8% of does [6]. The honest summary: very common in aged intact does, but the headline breed percentages reflect enriched historical colonies.

Can I just remove the ovaries, or do I need to take the cervices too?

Take the whole tract. Rabbits have two separate cervices and no common uterine body, and disease is often bilateral, so both uterine horns and both cervices should be removed; leaving uterine or cervical tissue risks recurrence. Ovariectomy alone does not address an existing endometrial lesion.

What is the prognosis once metastasis is present?

Grave. Metastasis develops within one to two years of the tumor becoming clinically detectable [2], and the classic interval from detection to death — usually after metastasis — is 12 to 24 months [8]. There is no established curative chemotherapy for the disease, so prevention and early surgery remain the meaningful interventions.

How does this compare with reproductive disease in other exotics?

The same principle — a high lifetime reproductive-tract disease burden in intact females — drives early elective spay recommendations across species. Merck frames uterine adenocarcinoma as the primary reason to spay non-breeding does [1], much as ovarian cystic disease drives management decisions in the guinea pig; see guinea pig ovarian cysts for that parallel.