Pyometra with Concurrent Endometrial Adenocarcinoma in Laboratory Opossums (Monodelphis domestica): A Case Series of Four Animals.

The use of laboratory opossums (Monodelphis domestica) in biomedical research has increased since the 1980s, when the first colonies were established in the United States, due to their relatively low maintenance requirements and cyclical breeding patterns resulting in reproductive efficiency. Despite their growing use, reproductive disorders in this species remain poorly characterized. A 2.5-year-old female laboratory opossum was euthanized for humane reasons after presenting lethargy, inappetence, and a severely distended abdomen. Gross necropsy revealed marked uterine enlargement. Cytologic evaluation demonstrated the presence of septic endometrial fluid, and aerobic bacterial culture yielded heavy growth of Escherichia coli and Stenotrophomonas maltophilia. Histopathologic examination confirmed suppurative endometritis (pyometra) with concurrent pyosalpinx and endometrial adenocarcinoma. Subsequently, 3 additional cases of pyometra were identified within the same colony, prompting further evaluation. These 4 affected animals (ages 2.1-2.52 years) were all from the PBP strain and demonstrated consistent clinical and reproductive features. Common findings included infertility or reduced reproductive success, abdominal distension, lethargy, and lumbosacral alopecia. To assess the novelty of this finding, a comprehensive literature search was conducted using Google Scholar, PubMed, ScienceDirect, and Web of Science, with keywords related to laboratory opossums, marsupials, and reproductive pathology. No prior reports describing histopathologic features of pyometra or associated neoplasia in M. domestica were identified. This case series suggests that pyometra may represent an underrecognized reproductive condition in laboratory opossums, potentially associated with age, reproductive history, and strain-specific factors. Recognition of these clinical patterns is important for colony health monitoring, reproductive management, and minimizing potential confounding effects on research outcomes.