Common Spontaneous Tumors and Tumor-like Lesions in 70 Pet Rodents and Negative MMTV Detection in Mammary Tumors

Compared to the number of studies on the neoplasms of laboratory rodents, fewer studies have focused on spontaneous neoplasms in pet rodents. Notably, the mouse mammary tumor virus (MMTV) is associated with mammary tumors in rodents. In this study, 77 tumors and tumor-like lesions of biopsy samples were collected from 70 pet rodents, including hamsters (n = 47), guinea pigs (n = 16), unknown species (n = 4), rats (n = 2), and a gerbil. Fifty tumors were collected from 47 hamsters, in which the most common tumors were mammary tumors (13/50), followed by fibrosarcoma (9/50), mast cell tumors (4/50), and squamous cell carcinoma (4/50). The collected subtypes of mammary tumors in hamsters included tubular carcinoma (n = 5), tubular adenoma (n = 4), carcinoma and malignant myoepithelioma (n = 1), simple tubular carcinoma (n = 1), adenosquamous carcinoma (n = 1), and tubulopapillary adenoma (n = 1). In addition, twenty tumors were collected from guinea pigs, in which the most common tumor was lipoma (6/20), followed by adenocarcinoma of the mammary gland (4/20), trichofolliculoma (2/20), and collagenous hamartomas (2/20). In guinea pigs, the subtypes of mammary gland tumors were tubular carcinoma (n = 2), tubular and solid carcinoma (n = 1), and tubulopapillary carcinoma (n = 1). In 20 cases of mammary tumors, MMTV was not detected, implicating no evidence of MMTV infection in mammary oncogenesis in pet rodents in Taiwan.

Lumpy, bumpy guinea pigs: a retrospective study of 619 biopsy samples of externally palpable masses submitted from pet guinea pigs for histopathology

Biopsy data on externally palpable masses in pet guinea pigs were retrieved from the archives of a large commercial pathology laboratory between November 2013 and July 2021. Of the 619 samples submitted from 493 animals, 54 (8.7%) had arisen from the mammary glands and 15 (2.4%) from the thyroid glands, with the remaining 550 (88.9%) involving the skin and subcutis, muscle (n = 1), salivary glands (n = 4), lips (n = 2), ears (n = 4) and peripheral lymph nodes (n = 23). Most of the samples were neoplastic, with 99 masses classified as epithelial in origin, 347 as mesenchymal, 23 as round cell, five as melanocytic and eight as unclassified malignant neoplasms. Lipomas were the most common neoplasm diagnosed, accounting for 286 of all samples submitted.

Endocrine Diagnostics for Exotic Animals

Endocrine disease in exotic species is less common than in small animals. Nevertheless, the diagnostic principles used in small animals can be adapted to evaluate endocrine disease in many of the exotic species although species-specific aspects need to be considered. This article covers important diseases such as thyroid dysfunction in reptiles and birds, hyperthyroidism in guinea pigs, and hyperadrenocorticism in ferrets. Glucose metabolism in neoplasms affecting normal physiology, such as insulinoma in ferrets and gastric neuroendocrine carcinoma in bearded dragons, is discussed. Calcium abnormalities, including metabolic bone disease in reptiles and hypocalcemia in birds, are also covered.

Research-Relevant Conditions and Pathology of Laboratory Mice, Rats, Gerbils, Guinea Pigs, Hamsters, Naked Mole Rats, and Rabbits

Animals are valuable resources in biomedical research in investigations of biological processes, disease pathogenesis, therapeutic interventions, safety, toxicity, and carcinogenicity. Interpretation of data from animals requires knowledge not only of the processes or diseases (pathophysiology) under study but also recognition of spontaneous conditions and background lesions (pathology) that can influence or confound the study results. Species, strain/stock, sex, age, anatomy, physiology, spontaneous diseases (noninfectious and infectious), and neoplasia impact experimental results and interpretation as well as animal welfare. This review and the references selected aim to provide a pathology resource for researchers, pathologists, and veterinary personnel who strive to achieve research rigor and validity and must understand the spectrum of "normal" and expected conditions to accurately identify research-relevant experimental phenotypes as well as unusual illness, pathology, or other conditions that can compromise studies involving laboratory mice, rats, gerbils, guinea pigs, hamsters, naked mole rats, and rabbits.

Updates on Thyroid Disease in Rabbits and Guinea Pigs

Hyperthyroidism seems to be a rare, but likely underdiagnosed disease of guinea pigs (Cavia porcellus) and rabbits (Oryctolagus cuniculus). Diagnosis is confounded by nonspecific clinical signs, lack of validated assays, and species-specific reference intervals. With increasing English-language publications on the topic, naturally occurring thyroid disease is likely to be increasingly diagnosed in exotic small mammals. The most consistently observed clinical signs include weight loss with or without a change in appetite and a palpable cervical mass. Diagnosis is supported by elevated blood thyroxine concentrations. Treatment may include thyreostatic agents, radioactive iodine, or surgical thyroidectomy.

Pathology of Diseases of Geriatric Exotic Mammals

The review covers select disease conditions most frequently described in aging rodents (rats, mice, hamsters, guinea pigs), rabbits, and ferrets. The conditions are categorized by general organ systems, infectious diseases, and neoplasms. Two data systems, the Veterinary Medical Teaching Hospital and Comparative Pathology Laboratory at the University of California, Davis and Zoo/Exotic Pathology Service, Citrus Heights, California were used in the determining disease conditions to describe.

Thyroid Adenoma and Ectopic Thyroid Carcinoma in a Guinea Pig (Cavia porcellus)

A 56-mo-old male guinea pig (Cavia porcellus) presented with gradual weight loss from 757 to 691 g during the preceding month. Cardiac-specific diagnostics detected decreased cardiac contractility, moderate cardiomegaly, pericardial effusion, and pulmonary edema. At 1 mo after presentation, the guinea pig died while under treatment. Necropsy revealed a 5 × 3 × 3-mm, tan, smooth nodule on the base of the heart. On histology, the nodule contained moderately cellular neoplastic tissue comprising cuboidal cells arranged in variably sized follicles. Immunohistochemically, the neoplastic cells were positive for thyroglobulin and thyroid transcription factor 1, consistent with ectopic thyroid carcinoma. Other significant histologic lesions included thyroid adenoma of the right thyroid gland, myocardial hypertrophy and degeneration, suppurative bronchopneumonia, and centrilobular hepatocellular degeneration. Although serum total thyroxine concentration was not evaluated, we considered that the tumors in this case were functional because concurrent lesions related to hyperthyroidism were present. In guinea pigs, reports of endocrine tumors, including thyroid tumors, have been increasing. To our knowledge, the current report represents the first documentation of ectopic thyroid carcinoma in this species.

HISTOPATHOLOGIC CHARACTERISTICS OF THYROID GLAND NEOPLASMS IN THOMSON'S GAZELLES ( EUDORCUS THOMSONII)

Published reports of neoplasms in Thomson's gazelles ( Eudorcas thomsonii) are very rare, but thyroid tumors were the most common neoplasm of this species, accounting for 12% of reported pathologies in a 1998-2012 retrospective study of cases submitted for histologic review of grossly enlarged thyroid glands. This report describes the histological and immunohistochemical characteristics of thyroid neoplasms in 10 Thomson's gazelles from five different zoological collections. Neoplasms were submitted as biopsies from six gazelles or collected during necropsy from four gazelles. The most common clinical findings included a palpable mass on the ventral neck and progressive weight loss. Radiographic mineral density was detected in one of the neoplastic masses. Histologically, the neoplasms were classified as microfollicular thyroid adenoma ( n = 2), solid thyroid adenoma ( n = 2), papillary thyroid adenoma ( n = 1), and solid thyroid carcinoma ( n = 5). Neoplastic cells in all 10 neoplasms were positive for thyroid transcription factor 1 and thyroglobulin, but negative for calcitonin. While five cases had histologic features of malignancy, there was no evidence of metastatic disease either clinically (biopsies) or on necropsy. Numerous concurrent diseases, including cardiomyopathies and nephropathies, were present and led to choice for euthanasia in several cases.

Rodent Oncology: Diseases, Diagnostics, and Therapeutics

Cancer incidence in rodent species varies dramatically from a common occurrence in mice and rats to just a limited number of documented cases in chinchillas and degus. This article summarizes common tumors, both benign and malignant, that have been reported to occur in rodents. Outlined are clinical signs, diagnostics, and treatments that have been described for rodents presenting with specific neoplasms.

Spontaneous reproductive pathology in female guinea pigs

Reproductive pathology of domestic guinea pigs is underreported to date. To provide a comprehensive review of uterine disease in guinea pigs, we performed a retrospective study of the pathology archives of the University of Tennessee, College of Veterinary Medicine. By histology, 13 of 37 uterine lesions in 23 animals were neoplastic; the other 24 nonneoplastic lesions included cystic endometrial hyperplasia (16 of 24), endometrial hemorrhage (3 of 24), pyometra (2 of 24), polyp (2 of 24), and mucometra (1 of 24). The most common guinea pig uterine neoplasms were uterine leiomyomas (6 of 13), followed by adenomas (3 of 13) and leiomyosarcomas (1 of 13). Other neoplasms included anaplastic tumors of unknown origin (2 of 13) and choriocarcinoma (1 of 13). Both anaplastic tumors and the choriocarcinoma were positive for vimentin. The choriocarcinoma was positive for HSD83B1, indicating a trophoblastic origin and its final diagnosis. All were negative for cytokeratin and smooth muscle. In multiple animals, more than 1 tumor or lesion was reported. Estrogen receptor and progesterone receptor expression was nearly 100% in uterine neoplasms. Nearly all animals for which data were available had cystic rete ovarii (18 of 19); the animal with no cystic rete ovarii had paraovarian cysts. In our study, female pet guinea pigs had a tendency to develop cystic endometrial hyperplasia and uterine neoplasia. Factors for the development of these lesions could be cystic rete ovarii, hormone dysregulation, and/or age. Other factors could contribute to the development of uterine lesions. As in other species, early ovariohysterectomy could decrease the prevalence of uterine lesions.

Thyroid diseases in rodent species

There are an abundance of studies of thyroid disease in rodents in a laboratory setting; however, research is limited in pet rodent populations. Validated reference intervals for thyroid testing are scarce, making interpretation of blood work difficult. Hyperthyroidism and hypothyroidism have been reported in multiple rodent species, with the most data available for guinea pigs. Thyroid neoplasia has been reported in the most common rodent species, although often as an incidental finding at necropsy. Further research is needed to determine frequencies of disease, methods of diagnosing, and treatment options with the best efficacy.