Thymomas are tumors arising from the epithelial cells of the thymus, the organ behind the breastbone where immune cells called T lymphocytes mature. In goats, the thymus has paired cranial and cervical lobes plus a single thoracic lobe, and tumors can develop in the cranial mediastinum, the space between the lungs, or in the ventral neck region. Post-mortem surveys suggest thymomas make up roughly ten percent of all tumors in goats, and dairy breeds such as Nigerian Dwarf and Saanen may carry an even higher prevalence, with one classic study reporting rates as high as twenty-five percent. Despite how common they appear to be at necropsy, almost nothing has been published about actually treating them.

The goat arrived at the University of Florida Large Animal Hospital after several days of lethargy, fever, and reduced appetite. On examination she was febrile at 106.2 degrees Fahrenheit, with rapid heart and respiratory rates, hyperemic mucous membranes, poor rumen contractions, and a heart murmur. Bloodwork revealed elevated fibrinogen and creatine kinase, low protein and calcium, and abnormalities on venous blood gas. A point-of-care thoracic ultrasound uncovered the likely culprit: a mass in the cranial mediastinum, alongside B-line artifacts and small areas of consolidation in the front of the chest that pointed to pneumonia.

A computed tomography scan performed under general anesthesia characterized the mass in detail. It measured 8.6 by 6.5 by 6 centimeters, appeared heterogeneous in soft tissue and fluid attenuation, and enhanced strongly with contrast. The tumor was displacing the cranial vena cava caudodorsally, pushing the heart backward, and compressing the cranial lung lobes, but there was no vascular invasion. Ultrasound-guided fine-needle aspiration yielded lymphoid tissue with poorly preserved epithelial cell aggregates and occasional mast cells, findings most consistent with a neoplasm of thymic origin, suspected to be a thymoma. The team also identified patterns consistent with aspiration or chronic bronchopneumonia and treated the goat empirically with florfenicol.

Treatment options were weighed carefully with the owner. Surgical excision was declined because of the substantial risk of intraoperative hemorrhage, a complication that has proven fatal in the only two goats previously reported to undergo thoracic surgery for mediastinal thymoma. Radiation therapy was offered instead, with candid discussion of acute risks including pneumonitis, esophagitis, tracheitis, and myocarditis, and late risks such as cardiomyopathy, arrhythmia, and lung fibrosis. The owner elected a palliative-intent protocol of four weekly fractions of 8 Gy, totaling 32 Gy, a schedule chosen to reduce costs and minimize the number of hospital visits and anesthetic episodes.

The technical execution of the plan illustrates how far veterinary radiation oncology has come. The goat was positioned in sternal recumbency in a vacuum-sealed cushion for a planning CT scan. The contrast-enhancing mass was contoured as the gross tumor volume, expanded uniformly by 2 millimeters to create the planning target volume. Because thymomas typically move little with respiration, no internal target volume was used, and the small margin prioritized sparing nearby organs at risk: the lungs, heart, esophagus, trachea, and spinal cord. An inverse-planned intensity-modulated plan with eight coplanar isocentric beams was generated on the Eclipse planning system, normalized so that 95 percent of the target received the full prescription dose, with only 5.6 percent of lung volume receiving 20 Gy or more.

Quality assurance was rigorous. The plan was verified with a two-dimensional diode array, requiring at least 95 percent of measured points to agree with the calculated fluence at a 3 percent and 3 millimeter criterion. Treatment was delivered with 6 MV photons from a Varian Edge linear accelerator equipped with a 120-leaf multileaf collimator, and cone-beam CT scans taken before each session confirmed accurate positioning. Each fraction required general anesthesia, induced with propofol after butorphanol and midazolam premedication and maintained on isoflurane, with no complications. By the fourth fraction, the cone-beam CT already showed the tumor shrinking by roughly 5 millimeters in every dimension, and the goat’s appetite had returned to normal while her heart murmur had quieted.

The response endured. A recheck CT scan four months after treatment, performed during an unrelated emergency visit for fever and lethargy, showed the mass had shrunk to 6 by 4.6 by 5.2 centimeters, a 30 percent reduction that meets the formal definition of a partial response under Veterinary Cooperative Oncology Group RECIST criteria. The pulmonary changes seen before treatment had nearly resolved. A scan at ten months confirmed a persistent partial response, though it also revealed mild progression of lower airway inflammation and bronchopneumonia that the authors could not rule out as a low-grade late radiation effect or unrelated chronic bronchitis. Twenty months out, the owner reported only occasional mild coughing, and the goat was still alive at the time of manuscript submission, roughly 1,230 days after treatment began.

The result carries weight because the comparative literature is so thin. Only one previous goat with a cranial mediastinal thymoma had been treated with radiation, receiving 32 Gy in 4 Gy fractions every other day, with tumor regression noted by the sixth fraction and survival of at least 1.5 years. In dogs and cats, surgery remains the treatment of choice for thymoma, though perioperative mortality approaches 20 percent, and radiation produces overall response rates of 33 to 75 percent with median survival times of 5 to 8 months in dogs and 24 months in cats. Because metastasis is rarely seen in caprine thymoma, local control is the central therapeutic goal in goats as well, making radiation an attractive alternative when thoracic surgery is too risky or unavailable.

The authors acknowledge limitations, most notably that the diagnosis rested on cytology rather than the histopathology required for definitive confirmation of thymoma. They also note that the link between the goat’s pneumonia and the tumor is uncertain; in dogs, thymoma-associated megaesophagus drives aspiration pneumonia, but myasthenia gravis appears far less common in goats, and no megaesophagus was seen on CT. Still, the message is clear. As goats increasingly live as companion animals rather than production livestock, cancer care becomes a relevant expectation for their owners, and this case demonstrates that modern, image-guided, hypofractionated radiation therapy is technically feasible in goats, was well tolerated, and can produce objective, durable tumor shrinkage. Larger cohorts will be needed before firm recommendations can be made, but for pet goats facing inoperable mediastinal thymoma, radiation therapy now stands as a legitimate option to discuss.

Subject of Research: Palliative hypofractionated image-guided intensity-modulated radiation therapy for a cranial mediastinal thymoma in a Nigerian Dwarf goat

Article Title: Image-guided intensity-modulated radiation therapy for a mediastinal thymoma in a Nigerian Dwarf goat: a case report

Article References: Argenti, T., Jodzio, D., Hancock, K., Darby, S., Luethy, D., Gilor, S., Gutti, J., & Takada, M. (2026). Image-guided intensity-modulated radiation therapy for a mediastinal thymoma in a Nigerian Dwarf goat: a case report. Veterinary Oncology, 3(1), Article 4. https://doi.org/10.1186/s44356-026-00055-6

Image Credits: AI Generated

DOI: 10.1186/s44356-026-00055-6

Keywords: thymoma, goat, radiation therapy, IMRT, veterinary oncology, Nigerian Dwarf goat, mediastinal mass, hypofractionated radiation, computed tomography, palliative care, caprine neoplasia, partial response