What types of tumors occur in rats? - briefly
Rats develop spontaneous and chemically‑induced neoplasms, chiefly mammary adenocarcinomas, pituitary adenomas, Leydig cell tumors, hepatocellular adenomas, and soft‑tissue or bone sarcomas. Additional common lesions include thyroid C‑cell hyperplasia, lymphomas, and renal tubule adenomas.
What types of tumors occur in rats? - in detail
Rats develop a wide spectrum of neoplasms that can be classified by tissue origin, anatomical location, and etiology. The most frequently observed spontaneous lesions include:
- Mammary gland adenocarcinomas – epithelial tumors arising in the abdominal mammary pads, common in older females.
- Pituitary adenomas – usually acidophilic or basophilic cell types, often asymptomatic but can cause endocrine disturbances.
- Liver hemangiosarcomas – malignant vascular tumors, prevalent in certain strains and associated with chronic exposure to carcinogens.
- Lung adenocarcinomas – arising from alveolar epithelium, frequently induced by inhaled toxicants.
- Skin squamous cell carcinomas – develop on the dorsal or ventral skin, often linked to ultraviolet radiation or chemical irritants.
- Uterine leiomyomas and leiomyosarcomas – smooth‑muscle neoplasms of the uterus, occurring in mature females.
- Testicular interstitial cell tumors – Leydig cell tumors, common in males, may produce hormones.
- Gastrointestinal stromal tumors (GISTs) – mesenchymal neoplasms of the stomach and intestine, characterized by c‑Kit expression.
- Renal tubular adenocarcinomas – malignant epithelial tumors of the kidney, observed in aged animals.
- Thymic lymphomas – lymphoid malignancies of the thymus, especially in certain inbred strains.
In addition to spontaneous forms, experimentally induced tumors expand the spectrum:
- Chemical carcinogen‑induced sarcomas – e.g., methylcholanthrene producing fibrosarcomas in subcutaneous tissue.
- Hormone‑driven mammary tumors – induced by estrogen or prolactin administration, mirroring human breast cancer pathology.
- Genetically engineered models – transgenic rats carrying oncogenes (e.g., KRAS, MYC) develop specific tumor types such as pancreatic ductal adenocarcinoma or glioma.
Histopathological classification follows the International Classification of Rodent Tumors (ICRT). Tumors are grouped into epithelial, mesenchymal, neuroectodermal, and hematopoietic categories, each with subtypes defined by cellular morphology, growth pattern, and immunohistochemical markers. For instance, epithelial neoplasms include adenomas, adenocarcinomas, and carcinoma in situ, while mesenchymal lesions comprise fibrosarcomas, liposarcomas, and osteosarcomas.
Epidemiological data indicate that tumor incidence increases with age, varies by strain, and is influenced by sex hormones. Certain strains, such as Sprague‑Dawley and Wistar, display higher rates of mammary and pituitary tumors, whereas Fischer 344 rats are prone to lymphomas and hepatocellular carcinomas.
Understanding the diversity of rat neoplasms is essential for toxicological assessment, pharmacological testing, and comparative oncology research. Accurate identification of tumor type, location, and biological behavior informs risk evaluation and therapeutic development.