Clinical presentation and treatment of lymphoma in companion rats (Rattus norvegicus; 2008-2020).

Objective: To describe the clinical presentation, treatment, and treatment outcomes for companion rats (Rattus norvegicus) diagnosed with lymphoma.
Animals: All rats that presented to the exotics service and underwent postmortem examination during the time period of 2008 through 2020 were evaluated.
Procedures: The medical records of 35 rats were evaluated for an ante- or postmortem diagnosis of lymphoma. Cases with a diagnosis of lymphoma were further reviewed for signalment, presenting complaint, clinical signs observed on physical exam, diagnostic testing performed, and treatments administered. Postmortem gross and histologic findings were reviewed.
Results: 7 out of 35 rats were diagnosed with lymphoma, either ante-mortem or postmortem. The most common presenting complaint that was present in all rats with lymphoma was respiratory abnormalities. Five out of 7 rats had radiographs performed, all of which had abnormalities noted in the thoracic cavity including pulmonary nodules, cranial mediastinal widening, or alteration to the cardiac silhouette. Diagnosis via cytologic aspirates was performed in 2 cases and each was diagnostic for lymphoma; however, even with treatment, survival time following initiation of chemotherapy was short (less than or equal to 24 days). The definitive diagnosis in the remainder of the cases was via necropsy.
Clinical Relevance: Results suggest that lymphoma is a common neoplastic disease in rats and a thorough diagnostic work-up is indicated in any rat that presents for general malaise or respiratory signs.