Neuroendocrine Tumours in Dogs: Insulinomas, Pheochromocytomas, and More

Oct 02 • 10 min read

Your vet felt something unusual during a routine exam near your dog's adrenal gland, or maybe your dog has been having strange episodes of weakness and confusion that resolve after eating, and now the word "neuroendocrine tumor" has come up. It's an unfamiliar term for most pet parents, but it actually covers a group of tumors that can show up in several very different places in your dog's body, each with its own signs and treatment path.

Neuroendocrine tissue tumors develop from cells that have both nervous system and hormone-producing functions, and they can occur in the adrenal or thyroid glands, the digestive tract, or the pancreas. These tumors can be benign or malignant, and even when benign, a growing tumor can disrupt nearby normal tissue and, in some cases, secrete excess hormone that causes its own set of problems.

Key Takeaways

Neuroendocrine tissues combine nervous system and hormone-producing functions and are found in several locations throughout the body.
Tumors in this tissue can be benign or malignant, and even benign tumors can cause problems simply by growing and pressing on nearby structures.
Insulinomas, gastrinomas, and glucagonomas are neuroendocrine tumors that develop specifically in the pancreas.
Pheochromocytomas develop in the adrenal medulla, the inner part of the adrenal gland.
Chemodectomas (tumors of the aortic and carotid bodies) are seen most often in brachycephalic breeds like Boxers and Boston Terriers.
Treatment options vary by tumor type and location, ranging from surgery to radiation, chemotherapy, or medical management, and often depend on referral to a specialist.

What Makes a Tumor "Neuroendocrine"?

Neuroendocrine tissues are tissues that combine two functions at once: nervous system activity and hormone production. These tissues turn up in a number of locations throughout the body, which is exactly why neuroendocrine tumors can look so different depending on where they arise. Tumors develop occasionally from neuroendocrine cells in the adrenal or thyroid glands, the digestive tract, or the pancreas.

These tumors can be benign or malignant. Even a benign tumor isn't necessarily harmless, though, since a growing mass can disrupt nearby normal tissue purely through physical pressure, and in some cases the tumor cells themselves secrete excess hormone, which creates a whole separate set of clinical signs tied to whatever hormone is being overproduced.

Pancreatic Neuroendocrine Tumors: Insulinomas, Gastrinomas, and Glucagonomas

Several types of neuroendocrine tumors develop specifically in the pancreas. Insulinomas arise from the insulin-producing cells and can cause dangerously low blood sugar by secreting excess insulin, leading to signs like weakness, disorientation, or seizures, especially around exercise or fasting. Gastrinomas secrete excess gastrin, a hormone that drives stomach acid production, which can lead to chronic stomach ulcers and related digestive signs. Glucagonomas are rarer still and involve excess glucagon secretion, which can affect blood sugar regulation in the opposite direction from insulinomas.

Because these pancreatic tumors are functional, meaning they actively secrete hormones, their signs often trace directly back to whatever that hormone does in the body, which can make the underlying tumor easier to suspect once the hormonal pattern is recognized.

Pheochromocytomas: Tumors of the Adrenal Medulla

Pheochromocytomas develop in the medulla, the inner part of the adrenal gland responsible for producing adrenaline-related hormones. These are relatively rare tumors, most commonly reported in dogs among domestic species, though clinical signs tend to be nonspecific, which can make them genuinely challenging to diagnose without a high index of suspicion.

When surgery is planned for a pheochromocytoma, pretreatment with a medication called phenoxybenzamine for around 12 weeks beforehand has been shown to improve the perioperative mortality rate, since it helps manage the dramatic blood pressure swings these tumors can cause during surgery. Dogs without evidence of tumor spread (metastatic disease) generally have a good long-term prognosis following appropriate treatment.

Thyroid C-Cell Tumors

Tumors that develop from C-cells in the thyroid gland occur less often than other types of thyroid tumors, and importantly, they're less likely to spread to other parts of the body compared to some other thyroid tumor types. Diarrhea is the most common sign associated with these tumors. In dogs, these tumors are often recognized as a palpable mass in the neck, and because they tend to be well encapsulated without a strong tendency toward metastasis, they're often good candidates for surgical removal. Treatment options for thyroid C-cell tumors can include surgery, radiation, chemotherapy, and radioactive iodine, depending on the specific case.

Chemodectomas: Tumors of the Aortic and Carotid Bodies

Illustration comparing functional and non-functional neuroendocrine tumors in dogs

Chemoreceptor organs are also derived from neuroendocrine tissue. These small structures can detect very small changes in the carbon dioxide and oxygen content and pH of the blood, helping regulate breathing and circulation. Tumors in this chemoreceptor tissue, called chemodectomas, usually develop in either the aortic body (located in the chest, near the base of the heart) or the carotid bodies (located in the neck).

These tumors are seen most often in brachycephalic breeds of dogs, such as Boxers and Boston Terriers, and a genetic predisposition combined with chronic low oxygen exposure has been suggested as a possible explanation for this breed pattern. Unlike the functional pancreatic tumors described earlier, chemodectomas don't secrete excess hormone, but they can still cause real problems by placing physical pressure on the heart, blood vessels, and nerves nearby. Aortic body tumors are more common than carotid body tumors, but they're actually less likely to spread to other parts of the body.

How Are Neuroendocrine Tumors Diagnosed?

Because these tumors can show up in so many different locations with such different signs, diagnosis usually starts with a thorough physical exam and a careful look at whatever signs prompted the visit in the first place, whether that's an episode of weakness, chronic digestive upset, a palpable mass, or something found incidentally during imaging for another reason. Blood tests can sometimes reveal a hormonal pattern consistent with a specific type of functional tumor, such as very low blood sugar with an insulinoma. Imaging, including ultrasound, x-rays, or more advanced techniques, is often used to locate a suspected mass and assess whether it may have spread. In many cases, a definitive diagnosis requires examining tissue directly, through biopsy or after surgical removal, under a microscope.

Treatment Depends Heavily on Type and Location

There's no single treatment protocol for neuroendocrine tumors, since so much depends on where the tumor is, what type it is, and whether it has already spread. Surgery is frequently the primary treatment when the tumor can be safely accessed and removed, sometimes combined with radiation, chemotherapy, or targeted medication depending on the specific tumor type. For tumors like pheochromocytomas, careful pre-surgical medical management can meaningfully improve the safety of the procedure itself. For tumors like insulinomas that aren't surgically removable, ongoing medical management, including dietary strategies and medication, can sometimes keep signs controlled even without removing the tumor outright.

Given how varied treatment can be, referral to a veterinary oncologist or internal medicine specialist is often part of the plan, particularly for functional tumors or ones in surgically tricky locations.

What This Means for Pet Parents

Infographic summarizing the main types of neuroendocrine tumors in dogs

If your vet has mentioned a possible neuroendocrine tumor, it's worth remembering that this is a broad category covering quite different conditions with quite different outlooks. A well-encapsulated thyroid C-cell tumor found early carries a very different prognosis than a pheochromocytoma that's already spread. The right next steps, further blood work, imaging, biopsy, or specialist referral, depend entirely on where your vet suspects the tumor is located and what signs your dog is showing. Bringing a clear, detailed account of your dog's symptoms, including anything that seems tied to eating, exercise, or specific times of day, can genuinely help your vet narrow down which type of neuroendocrine tumor is most likely before further testing even begins.

FAQ Section

What is a neuroendocrine tumor in a dog?
A neuroendocrine tumor develops from neuroendocrine tissue, which combines nervous system and hormone-producing functions. These tumors can occur in the adrenal or thyroid glands, digestive tract, or pancreas, and they can be benign or malignant, sometimes secreting excess hormone that causes its own distinct set of signs.

What is an insulinoma, and why is it dangerous?
An insulinoma is a neuroendocrine tumor of the pancreas that secretes excess insulin, which can cause dangerously low blood sugar. This can lead to weakness, disorientation, or seizures, often triggered around exercise or fasting, since these situations naturally lower blood sugar further.

Which dog breeds are prone to chemodectomas?
Chemodectomas, tumors of the aortic and carotid bodies, are seen most often in brachycephalic breeds of dogs, such as Boxers and Boston Terriers. A genetic predisposition combined with chronic reduced oxygen levels has been suggested as a possible explanation for this pattern.

Are neuroendocrine tumors always cancerous?
No. These tumors can be benign or malignant. Even a benign tumor, though, can still cause problems by growing and pressing on nearby normal tissue, or by secreting excess hormone if it's a functional tumor type.

How are neuroendocrine tumors in dogs treated?
Treatment varies significantly depending on the tumor's type and location. Surgery is often the primary approach when the tumor can be safely removed, sometimes alongside radiation, chemotherapy, or targeted medication. Some tumors, like certain insulinomas, can be managed medically even when surgical removal isn't possible.