Rabbit tumor case highlights risks of sex misidentification
Bottom line
A case report published online April 27 in the Journal of Veterinary Diagnostic Investigation describes a 5-year-old Holland Lop rabbit that had been presumed male, based on a small penis-like structure and pet store information, but was later found to have a malignant paramesonephric, or Müllerian, tumor associated with uterine-like tissue. Imaging showed a large caudal abdominal mass, exploratory surgery led to excision, and histopathology plus immunohistochemistry supported the diagnosis. PCR testing did not detect Y-linked genes including SRY, ZFY, and RBMY, suggesting the rabbit was genetically female. No gonadal structures were identified on imaging or during surgery. The rabbit initially improved after surgery, then died two weeks later from severe rhinitis rather than the tumor itself. (journals.sagepub.com)
Why it matters: For veterinary professionals, the report is a reminder that reproductive tract disease in rabbits can be missed when sex has been incorrectly assigned, especially in patients with atypical external anatomy or incomplete history. That matters because uterine neoplasia is already a major concern in intact female rabbits, with standard references describing uterine adenocarcinoma as the most common tumor in rabbits and recommending attention to reproductive disease as rabbits age. This case broadens the differential list beyond the more familiar uterine adenocarcinoma and highlights the value of correlating imaging, surgical findings, histopathology, and, when anatomy is unclear, molecular sex testing. (journals.sagepub.com)
What to watch: Whether this report prompts more routine use of confirmatory sex determination, including imaging or genetic testing, in rabbits with atypical genital findings or unexplained caudal abdominal masses. (journals.sagepub.com)
A newly published rabbit case report is drawing attention to a diagnostic blind spot in exotic practice: reproductive tumors can be overlooked when a patient’s sex has been misidentified. In the paper, published online April 27 in the Journal of Veterinary Diagnostic Investigation, clinicians describe a 5-year-old Holland Lop rabbit that had long been presumed male, but was ultimately diagnosed with a malignant paramesonephric, or Müllerian, tumor after workup of anorexia, lethargy, and a large caudal abdominal mass. (journals.sagepub.com)
What makes the case notable is the mismatch between presumed sex and internal pathology. According to the abstract, the rabbit had been labeled male based on a small penis-like structure and information from the pet store. Imaging later identified a mass separate from the bladder and rectum, and exploratory laparotomy found that it was associated with uterine-like structures, which were removed. Histopathology and immunohistochemistry were consistent with a malignant paramesonephric tumor. PCR testing failed to detect the Y-linked genes SRY, ZFY, and RBMY, supporting the conclusion that the rabbit was genetically female, even though no gonadal structures were found on imaging or at surgery. (journals.sagepub.com)
The report also lands in a broader clinical context. Reproductive tract disease is already a well-established concern in rabbits, particularly intact females as they age. Standard veterinary references describe uterine adenocarcinoma as the most common tumor in rabbits, with some sources reporting high prevalence in older intact does and advising routine surveillance or preventive spaying. That makes this case unusual not because reproductive tumors are rare in rabbits overall, but because the tumor type was uncommon and the patient’s apparent sex likely delayed recognition of a reproductive origin. (pmc.ncbi.nlm.nih.gov)
There is also a limited but relevant pathology history here. Earlier literature has documented malignant mixed Müllerian tumors in rabbits, including a 2006 case report described by its authors as the first reported rabbit case, and a later report of a uterine heterologous malignant mixed Müllerian tumor in a dwarf rabbit with metastases. The new paper adds a different layer by combining clinical presentation with histologic, immunohistochemical, and molecular sex-testing findings in a rabbit initially thought to be male. In that sense, the contribution is less about establishing that Müllerian tumors can exist in rabbits and more about showing how disorders of sexual development, atypical anatomy, or simple mis-sexing can complicate oncology workups. (pubmed.ncbi.nlm.nih.gov)
No formal outside commentary on this specific paper was readily available in the initial coverage reviewed, but the clinical implications align with longstanding rabbit medicine guidance: blood-tinged urine, abdominal enlargement, reduced appetite, or lethargy in an older rabbit should not be treated as straightforward urinary disease until reproductive causes are considered. Published imaging work has also supported radiography as useful in evaluating uterine disorders in sexually intact female rabbits, reinforcing the practical point that reproductive tract imaging deserves a place in the workup of caudal abdominal masses. Here, the challenge was that the patient was not thought to be female in the first place. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For veterinarians, this case is a reminder to separate recorded sex from confirmed sex when the history is uncertain or anatomy is atypical. In rabbit practice, sexing errors are not unheard of, particularly in younger animals or when external genital anatomy is ambiguous. This report suggests that when clinical signs point to a pelvic or caudal abdominal process, reproductive differentials should stay on the table even if the chart says “male.” It also underscores the diagnostic value of layered confirmation, including imaging, surgical exploration, pathology, immunohistochemistry, and, in selected cases, molecular testing. That approach may be especially relevant for exotic and small mammal clinicians who see delayed presentations after pet store purchase or incomplete early veterinary records. (journals.sagepub.com)
The outcome in this case was mixed. The rabbit improved initially after surgery, but died two weeks later from severe rhinitis, according to the report. Even so, the case offers a useful teaching point for general practice, emergency, and exotic teams: if a rabbit presents with nonspecific illness and a caudal abdominal mass, the differential list should include reproductive pathology regardless of assumed sex, and clinicians may need to verify sex more rigorously than history alone allows. (journals.sagepub.com)
What to watch: The next question is whether reports like this shift clinical protocols, particularly around intake sex verification, imaging of unexplained pelvic masses, and selective use of genetic testing in rabbits with ambiguous anatomy or discordant reproductive findings. (journals.sagepub.com)