What ails the pet rat? A retrospective study of more than 300 biopsy samples of externally palpable masses submitted from pet rats for histopathology (2013–2021).

Biopsy data on externally palpable masses in pet rats (Rattus norvegicus) were retrieved from the archives of a large commercial pathology laboratory between November 2013 and July 2021. A total of 330 samples were submitted from 292 individual animals. Of the 330 samples submitted, 182 (55.2%) were of mammary gland origin and the majority were benign neoplasms, with fibroadenoma most frequent. Of the remaining 148 samples, 101 were neoplastic in nature, with 76 tumours classified as mesenchymal, 23 as epithelial and two classified only as malignant neoplasia not otherwise specified. Malignant neoplasms accounted for 88 of these non-mammary masses, with the most diagnosed tumours including soft tissue sarcoma (including fibrosarcoma) and sarcomas not otherwise specified. [ABSTRACT FROM AUTHOR]