Uterine Adenocarcinoma in a Rabbit
History: An 11 year old intact female rabbit had a chronic history of Pasteurella multocida snuffles and head tilt which had resolved. Her owner noticed she started to have increased abdominal component of respiration which progressed to open mouth breathing. A mass was palpated in the caudal abdomen during examination.
The lungs were almost completely replaced by large numbers of individual to coalescing firm white nodules ranging in size from 0.5 cm to 3 cm in diameter and projecting 1-2 cm from the lung surface. On cut surface the nodules were firm and homogeneously white.
A 3.5 cm x 2 cm x 1 cm elliptical mass was present in the wall of the right uterine horn located approximately 1 cm from the ovary. The mass was irregular and composed of firm white nodules and softer grey areas.
The liver had multifocal firm white nodules (1.5 cm to 0.5 cm in diameter) scattered throughout the parenchyma.
Uterus: The myometrium was infiltrated by a neoplasm composed of epithelial cells forming tubules and acini.
Lung and Liver: The neoplastic cells in the lung and liver resembled those in the uterus, however they formed solid sheets rather than acini and were more anaplastic with marked anisocytosis and anisokaryosis.
Uterine adenocarcinoma arises from endometrial glands, and is the most common spontaneous neoplasm in Rabbits. The incidence of this neoplasm increases to 80% of animals 5-6 years and older in Oryctolagus cuniculus. The etiology of the neoplasm is unknown, however some reports implicate estrogen as a related factor. A recent report in Vet Pathol found that papillary adenocarcinomas were negative for both estrogen and progesterone receptors, but tubular/solid neoplasms were positive for either estrogen or progesterone receptors. The authors suggest that there may be a separate pathogenesis between these two forms of the neoplasm.
These tumors usually are multinodular and involve both uterine horns. They may metastasize to the lung and liver most commonly and become implanted on serosal surfaces of the abdominal organs.
Percy, DH and Barthold, SW. Chapter 6 Rabbit in Pathology of Laboratory rodents and rabbits, 3rd edition. p 253. Blackwell Publishing, 2007.