A 14-year-old Maine Coon cat with a massive, inoperable tumor wrapped around the carotid artery in its neck has become the first feline on record to be treated with stereotactic body radiotherapy for a suspected carotid body paraganglioma, and the outcome is remarkable. According to a case report published in the journal Veterinary Oncology, three carefully sculpted daily doses of high-dose radiation shrank the tumor rapidly, controlled the disease for more than two years, and produced almost no side effects beyond a patch of white fur. The report, led by veterinary radiation oncologist Patricia Gualtieri of Tufts University’s Cummings School of Veterinary Medicine with colleagues at Colorado State University, opens an entirely new treatment avenue for cats with advanced head and neck cancers that were previously considered untreatable.
The cat arrived at the Colorado State University Veterinary Teaching Hospital after its owner noticed a growing mass in the neck. Two weeks earlier, the family veterinarian had measured it at 3.7 by 2.1 centimeters, but by the time of the referral examination it had expanded to roughly 5 centimeters long and 4 centimeters wide, filling the ventral part of the neck. The owner also described six months of gradually worsening snoring noises, lethargy, and a mildly reduced appetite. On physical examination, the cat was bright and alert but showed intermittent stertor and stridor, the harsh breathing sounds produced when the upper airway is partially obstructed. A large, fixed, painless mass dominated the left side of the throat.
Advanced imaging revealed the true scale of the problem. A triple-phase computed tomography scan showed a lobular, strongly and heterogeneously enhancing soft tissue mass measuring 5.2 by 4.1 by 3.9 centimeters that completely enveloped the common carotid artery, the main vessel supplying the head. The mass compressed and displaced the thyroid glands, pushed the pharynx, larynx, and hyoid apparatus markedly to the right, and extended toward the skull base near the tympanic bulla. Multiple branching vessels penetrated deep into the tumor interior, a hallmark of the rich blood supply characteristic of chemoreceptor tissue. A board-certified radiologist judged the growth pattern inconsistent with thyroid carcinoma, and the differential diagnosis narrowed to a carotid body tumor, a metastatic lymph node mass, or a primary soft tissue sarcoma.
Fine-needle aspiration cytology of the mass showed an epithelial neoplasm with endocrine and neuroendocrine morphology: densely cohesive clusters of round to polygonal cells with scant basophilic cytoplasm, ropey chromatin, and absent nucleoli. Critically, immunocytochemical staining for Thyroid Transcription Factor-1, a marker of thyroid origin, came back negative, making a thyroid tumor far less likely. The absence of any secretory phenotype, no hyperthyroidism and no hypercalcemia on bloodwork, further separated this tumor from the functional thyroid and parathyroid carcinomas that typically arise in the feline neck. Taken together with the tumor’s location hugging the carotid bifurcation, the team concluded the mass was most consistent with a paraganglioma of the carotid body, a tumor type never before documented in a cat.
That diagnosis matters because carotid body paragangliomas, also called chemodectomas, arise from the chemoreceptor organs that sense oxygen and carbon dioxide in blood. They are well described in dogs and humans, in whom they are notoriously invasive, enveloping major vessels at the base of the skull and causing retropharyngeal masses, difficulty swallowing, respiratory distress, stridor, gagging, and laryngeal paralysis. This cat’s presentation, including left-sided laryngeal paralysis and bilateral tonsillar protrusion noted on a sedated oral exam, matched that pattern almost exactly. Yet in cats, paragangliomas had only ever been reported in the abdomen, around the kidneys and retroperitoneum, at the aortic body, in the heart, and in the orbit, never at the carotid body, despite the fact that cats possess these normal anatomic structures.
Surgery was off the table. After reviewing the imaging, a board-certified surgical oncologist judged the mass unresectable because of its extensive involvement of the carotid artery, larynx, and hyoid apparatus, and warned that any biopsy attempt risked catastrophic hemorrhage and airway-compromising swelling. The oncology team instead offered definitive-intent stereotactic body radiotherapy, a technique that delivers ablative radiation doses in a handful of fractions with submillimeter targeting. The rationale was technical as much as biological: compared with a conventional 16 to 20 fraction course, a three-fraction protocol meant only three anesthesia episodes for a cat that was already difficult to intubate, with far less cumulative acute toxicity to the pharynx and trachea.
The treatment plan was built on the treatment planning system using pre- and post-contrast CT sequences. The gross target volume encompassed all abnormal contrast-enhancing tissue and abnormal vasculature, including the left tonsil. A 2-millimeter planning target volume expansion accounted for setup uncertainty, but was cropped away from organs at risk, the skin, pharynx, trachea, esophagus, brain, spinal cord, and eyes, to prioritize normal tissue sparing. Two coplanar arcs of 6-megavolt photons delivered 10 Gy per day for three consecutive days, for a total of 30 Gy, using volumetric modulated arc therapy. Dosimetry was calculated with the Acuros algorithm, and quality assurance with an electronic portal imaging device achieved a gamma passing rate above 95 percent at 3 millimeters and 3 percent, confirming the planned dose distribution matched delivery.
The response was fast and durable. Two weeks after the final fraction, the tumor had shrunk roughly 30 percent in length and 37.5 percent in width on caliper measurement, the cat’s breathing signs had resolved, and its appetite had normalized. By three months, the mass was no longer palpable at all. Ultrasound at 15 months showed a residual soft tissue structure surrounding the left carotid artery, and a 24-month scan by a second radiologist documented a highly vascular mass measuring 3.2 by 2.2 centimeters, a persistent partial response under RECIST 1.0 criteria with no local or systemic progression for 755 days. Thyroid hormone values, which had been suppressed by euthyroid sick syndrome at presentation, returned to and remained within normal ranges through repeated monitoring.
Tolerability was equally striking. The only radiation-related adverse event was leukotrichia, whitening of the fur in the treatment field, graded as a mild VRTOG grade 1 late skin toxicity. A transient episode of hiding, drooling, and poor appetite after the first fraction resolved when gabapentin was stopped and an anti-nausea drug given. Later weight loss at 20 to 24 months was traced to newly diagnosed chronic kidney disease and a progressively enlarging hepatic cystadenoma, both judged unrelated to the cervical tumor or its radiation. At the time of manuscript submission, the cat was alive with no evidence of disease progression, more than two years after treatment.
The authors caution that without surgical histopathology, which was deliberately avoided given the hemorrhage risk, the diagnosis remains presumptive; cytology alone cannot fully exclude ectopic thyroid or parathyroid tumors, and the definitive classification would have required immunohistochemistry on tissue. Even so, the convergence of imaging, cytomorphology, TTF-1 negativity, and the non-secretory clinical picture makes carotid body origin the leading explanation. The team recommends that carotid body paraganglioma be added to the differential list for feline cervical neuroendocrine masses, and that endocrine function screening be built into both initial work-up and long-term follow-up, since radiation can induce endocrine changes, as seen in dogs. For veterinary oncologists facing cats with otherwise untreatable advanced neck tumors, the report suggests external beam radiotherapy, and stereotactic body radiotherapy in particular, can now be offered as a definitive local option rather than a palliative afterthought.
Beyond this single patient, the case fills a genuine gap in comparative oncology. In human medicine, carotid body paragangliomas are the most common head and neck paragangliomas, and while surgery remains the mainstay, definitive radiotherapy and stereotactic techniques are established alternatives for tumors encasing the carotid artery, where resection carries stroke risk. In dogs, these tumors are typically encountered as incidental, slowly growing masses at the heart base, and complete surgical excision is rarely achieved. The feline report suggests that the radiotherapy experience accumulated in those species may translate across species lines.
The diagnostic work-up also illustrates a subtlety of feline endocrinology. The cat’s low total thyroxine with inappropriately low thyroid-stimulating hormone was interpreted as euthyroid sick syndrome, a reversible suppression of thyroid hormone values caused by non-thyroidal illness, rather than true hypothyroidism. Recognizing this pattern prevented a misdiagnosis that could have steered the work-up toward thyroid disease, and the later normalization of thyroid values on follow-up confirmed the interpretation.
Finally, the durability of response matters for fractionation debates in veterinary radiation oncology. Ablative hypofractionated schedules trade convenience and reduced anesthesia exposure against uncertainty about late toxicity, and this report, with more than two years of follow-up and only grade 1 leukotrichia, provides early evidence that such schedules can be both effective and well tolerated in cats with deeply seated cervical disease.
Subject of Research: First reported use of stereotactic body radiotherapy to treat a suspected feline carotid body paraganglioma
Article Title: Locally advanced cervical neuroendocrine tumor of presumptive carotid body origin in a cat treated with stereotactic body radiotherapy (SBRT): a case report
Article References: Gualtieri, P., Benedict, W. M., Tremolada, G., & Boss, M.-K. (2026). Locally advanced cervical neuroendocrine tumor of presumptive carotid body origin in a cat treated with stereotactic body radiotherapy (SBRT): a case report. Veterinary Oncology, 3(1), Article 18. https://doi.org/10.1186/s44356-026-00071-6
Image Credits: AI Generated
DOI: 10.1186/s44356-026-00071-6
Keywords: cat, carotid body, paraganglioma, chemodectoma, neuroendocrine tumor, SBRT, stereotactic body radiotherapy, veterinary oncology, VMAT, cervical mass, TTF-1, radiation therapy
Cite Scienmag News
APA
MLA
Chicago
Nathaniel Bowman. (September 10, 2026). First-Ever Cat Treated for Rare Carotid Body Tumor With Precision Radiotherapy Survives More Than Two Years. Scienmag. https://scienmag.com/first-ever-cat-treated-for-rare-carotid-body-tumor-with-precision-radiotherapy-survives-more-than-two-years/
Nathaniel Bowman. “First-Ever Cat Treated for Rare Carotid Body Tumor With Precision Radiotherapy Survives More Than Two Years.” Scienmag, 10 September 2026, https://scienmag.com/first-ever-cat-treated-for-rare-carotid-body-tumor-with-precision-radiotherapy-survives-more-than-two-years/. Accessed 10 September 2026.
Nathaniel Bowman. “First-Ever Cat Treated for Rare Carotid Body Tumor With Precision Radiotherapy Survives More Than Two Years.” Scienmag. September 10, 2026. https://scienmag.com/first-ever-cat-treated-for-rare-carotid-body-tumor-with-precision-radiotherapy-survives-more-than-two-years/
Copy citation
Download RIS
Tags: advanced head and neck cancer in petscarotid bodycarotid paraganglioma in animalscatcervical masschemodectomafeline carotid body tumor treatmenthigh-dose radiation therapy in animalsinnovative cancer treatments in veterinary sciencelong-term survival in feline cancer patientsMaine Coon tumor treatmentneuroendocrine tumornon-invasive cancer therapies for catsparagangliomaradiation therapyrare tumor management in catsSBRTstereotactic body radiotherapystereotactic radiotherapy for catsTTF-1tumor control in veterinary medicineveterinary oncologyveterinary oncology case studyVMAT
