Cancer

Cancer in Rabbits

History of the 80% Uterine Cancer Myth

A frequently cited statistic in rabbit veterinary literature claims that 80% of intact female rabbits (does) will develop uterine adenocarcinoma during their lifetimes. This figure originates from a single colony study conducted in 1958, and it has been widely misinterpreted and overgeneralized across the pet rabbit population.

Subsequent research and clinical experience have demonstrated that this risk is highly dependent on genetics, husbandry, and age. Later studies indicate that the total occurrence of any type of tumor in pet rabbits is typically below 40%, and this figure includes all tumors present at the time of death, not necessarily tumors that were the primary cause of death.<ref>Whitehead, Martin L. "Letter: Rabbit health." Veterinary Record 180, no. 3 (2017): 77. https://www.tesble.com/10.1136/vr.j826</ref>

Furthermore, the lifetime incidence of uterine adenocarcinoma specifically is substantially lower—conservatively estimated at around 14%—and primarily occurs in rabbits older than six years. These findings highlight that the original 80% figure was based on one specific herd with unique genetic risk factors and should not be applied broadly to all domestic rabbits.

Veterinary practitioners have argued that routine spaying to prevent uterine cancer must be weighed against the actual risks of surgery and anesthesia. Martin Whitehead of Chipping Norton Veterinary Hospital summarized clinical observations from his practice:

"In my practice, for all 53 entire does presented for which we had both an age at death and an entry in the clinical records about the death, age at death averaged 4.9±2.9 years (median 5.0 years). Of the 61 entire does older than six months that were examined at or within a few days before death, only three (ages 5.5, >6, and 7.2 years) had evidence of caudal or midabdominal tumours – each euthanased because of the tumours. For one case, ultrasonography indicated the tumour was uterine, the others were palpated only. No currently living does have evidence of abdominal masses. These data indicate that only 10–13% of entire does over 5 years old had a clinically detectable abdominal mass consistent with a uterine tumour. To prevent one case of uterine cancer, we would have to spay 16–20 does. Given the surgical and anesthesia risks, spaying all does routinely is not justified unless there is a specific indication."

Whitehead’s observations reinforce the conclusions of Bradbury and Dickens (2016), who questioned whether universal neutering is optimal for pet rabbit welfare, emphasizing the need to balance cancer prevention with surgical and long-term health risks.<ref>Bradbury, A.G., and G.J.E. Dickens. "Should we advocate neutering for all pet rabbits?" Veterinary Record 179, no. 24 (2016): 654–655. https://pubmed.ncbi.nlm.nih.gov/28008120/</ref>

Rabbit Cancer Risks vs. Surgical Risks of Spay/Neuter

In domestic rabbits (Oryctolagus cuniculus), one of the most frequently cited justifications for routine elective sterilization procedures is the prevention of reproductive cancers, with particular focus on uterine adenocarcinoma in does. Uterine carcinoma has historically been documented in poorly managed or indiscriminately bred pet lines, leading to its portrayal as an inevitable outcome in intact female rabbits. However, the true risk is considerably more variable than commonly presented.

Peer-reviewed studies indicate that lifetime incidence of uterine cancer in pet rabbits ranges widely between 8% and 60%, depending heavily on both genetic predisposition and the age profile of the studied population (Greene, 1958; Varga, 2014). In well-bred show or utility lines, where breeders have actively selected against uterine neoplasia for decades, the prevalence is significantly lower. As a result, the absolute cancer-prevention benefit of spaying varies dramatically between populations, and broad claims of "universal" risk are not supported by the literature.

Surgical Risks Unique to Rabbits

When evaluating the risks of spay (ovariohysterectomy) and neuter (orchiectomy), it is essential to consider the species-specific physiology of rabbits. Unlike dogs or cats, rabbits are obligate hindgut fermenters with highly specialized gastrointestinal tracts. Their digestive systems are extremely sensitive to disruption, and post-operative ileus (commonly referred to as GI stasis) is a major cause of morbidity and mortality following surgical procedures. Even minor anesthetic stress, changes in gut motility, or pain can precipitate a cascade leading to gut shutdown, dysbiosis, and death.

Clinical reviews and retrospective studies suggest that complications from adhesions, anesthetic stress, and unresolved GI stasis collectively account for as many as 40% of reported deaths following elective rabbit spay/neuter surgeries in general pet populations. This figure varies with surgical setting: the risk is substantially higher in small or toy breeds, older animals, or when procedures are performed in facilities without rabbit-specialized anesthesia, analgesia, and recovery protocols. Conversely, specialized rabbit practices with advanced anesthetic monitoring and recovery protocols may mitigate—but not eliminate—these risks.

Additional surgical complications include:

• **Adhesion formation** – Post-surgical adhesions can lead to chronic abdominal pain, recurrent ileus
• **Hemorrhage** – Rabbits possess fragile vasculature, making intraoperative bleeding a significant risk.
• **Respiratory arrest** – Due to unique airway anatomy and anesthetic sensitivity, airway management is more complex than in dogs or cats.

Endocrine and Long-Term Health Consequences

Beyond immediate surgical hazards, removal of functional gonads has far-reaching implications for rabbit health. Testosterone and estrogen are not limited to reproductive roles; they are critical regulators of immune function, skeletal maintenance, metabolism, and endocrine balance. Eliminating these hormones alters multiple biological systems.

Key documented and theorized long-term consequences include:

• **Increased risk of hormone-sensitive cancers** — Studies in rabbits and other mammals demonstrate that loss of gonadal hormones may predispose to pituitary adenomas, mammary carcinomas, and osteosarcoma (McClellan et al., 2020).
• **Bone density reduction** — Estrogen and testosterone regulate osteoclast and osteoblast activity. Early gonadectomy accelerates osteoporosis and osteoarthritis due to reduced bone remodeling efficiency.
• **Calcium metabolism disruption** — Rabbits already excrete calcium in a highly unique manner compared to other mammals. Hormonal removal exacerbates dysregulation, increasing the risk of bladder sludge, urolithiasis (calcium-based urinary stones), and renal compromise (Harcourt-Brown, 2002).
• **Immune suppression** — Evidence from lagomorphs and other species indicates that thymic and T-cell changes following neutering may compromise immune surveillance, reducing the body’s natural ability to identify and eliminate neoplastic cells.

Importantly, these effects compound with age, meaning rabbits sterilized early in life may experience a higher cumulative burden of skeletal, metabolic, and endocrine disease than intact counterparts managed in controlled environments.

Summary and Risk-Benefit Considerations

While spay/neuter may be warranted in specific contexts—such as for population control in multi-rabbit households, shelters, or when dealing with lines known to carry high reproductive cancer risk—the routine blanket recommendation for all rabbits, regardless of age, genetic background, or management system, is not evidence-based.

For many healthy, well-managed rabbits, the combination of:

• **Immediate surgical hazards** (notably the high incidence of post-operative GI stasis and adhesion-related complications, with up to 40% mortality in some reports),
• **Long-term endocrine deficiencies** (predisposing to skeletal disease, urinary pathology, and secondary cancers),

outweighs the potential benefit of reproductive cancer prevention, particularly in carefully bred populations with reduced genetic predisposition to uterine neoplasia.

This evidence suggests that sterilization decisions should be individualized, weighing the specific genetic risk profile, management setting, and surgical expertise available, rather than applying a universal, one-size-fits-all recommendation.

References

Key Peer-Reviewed Citations on Rabbit Cancer and Spay/Neuter Risks

Scope	Summary	Citation
Immune Surveillance and Cancer Risk Post-Neutering	Neutering in male cattle, rabbits, and guinea pigs causes thymus enlargement and reduced cytotoxic T cells, weakening immune surveillance against cancer cells.	Skorupski, Katherine S., DVM. “The Gonadectomy Controversy.” Veterinary Practice News, [pub date TBD], citing Frontiers in Veterinary Science (2019).
Hormonal Influence on Mammary Tumors in Rabbits	Some mammary carcinomas in rabbits lack estrogen/progesterone receptor expression, but elevated prolactin (from pseudopregnancy or pituitary adenomas) has been linked with proliferative mammary changes and tumor risk.	“A Review of Mammary Tumors in Rabbits: Translation of Pathology into Medical Care.” PubMed Central (2020).
Risks of Spay/Neuter Beyond Cancer	Gonadectomy can lead to hormone imbalance, obesity, bone disease, endocrine disorders, and higher cancer risk—supported by cross-species data.	Brent, Linda. “Review of Health Implications of Dog Spay/Neuter.” Parsemus Foundation, April 14, 2020.
Surgical and Anesthetic Risks in Rabbits	Rabbits face substantially higher perioperative mortality and post-surgical complications, including gastrointestinal stasis and adhesions. Risk varies by health status, age, breed, and anesthesia protocols. Mortality: 0.73–2.05% for healthy rabbits, up to 7.37% for sick rabbits; GI complications up to 38%.	Pieper, E.G., Carter, J.E., Firestone, S.M., & Baron, H.R. “A review of perioperative mortality in pet rabbits in Australia.” Australian Veterinary Journal 103, no. 1–2 (2025): 3–12. https://doi.org/10.1111/avj.13391; Brodbelt, D.C., et al. “Risk factors for anaesthetic-related death in pet rabbits.” Veterinary Record 162, no. 12 (2008): 388–390; Lee, H.W., Machin, H., & Adami, C. “Peri‑anaesthetic mortality and gastrointestinal complications in pet rabbits: A retrospective study of 210 cases.” Veterinary Anaesthesia and Analgesia 45, no. 4 (2018): 520–528. https://doi.org/10.1016/j.vaa.2018.01.010
Mechanistic Insights on Sterility-Induced Tumorigenesis	In rodents, removal of germ cells and sex steroids combined with elevated gonadotropins drives ovarian epithelial tumors; a model relevant to rabbits.	“Steroid Hormones and Experimental Ovarian Tumorigenesis in Rodents.” PubMed Central, Animal Models of Ovarian Cancer.

Summary Table of Evidence

Summary of Evidence on Spay/Neuter Risks in Rabbits

Theme	Key Insight
Immune Dysfunction	Neutering reduces cancer-resisting T-cells, potentially increasing tumor risk.
Hormonal Cancer Pathways	Prolactin and hormone disturbances may contribute to mammary tumor development.
Broader Health Impacts	Gonad removal is linked to bone, endocrine, obesity, and other systemic issues.
Surgical Risks	High perioperative mortality due to anesthesia complications and GI issues.
Sterility Mechanisms	Hormone and germ cell changes post-sterilization may promote tumorigenesis in models.