What is the pancreas?
The pancreas is a glandular organ that is located close to the first part of the small intestine. It serves as two glands in one: a digestive exocrine gland and a hormone-producing endocrine gland. As such, it has two main types of cells: exocrine cells and endocrine cells. Exocrine cells produce enzymes that aid in digestion and endocrine cells produce hormones that control body functions. The hormones insulin and glucagon control blood sugar (glucose) levels, and the hormone gastrin controls the secretion of gastric acid (HCl) in the stomach.
What is a pancreatic tumor?
A pancreatic tumor is an abnormal proliferation and dysregulated replication of cells within the pancreas. There are two groups of pancreatic tumors: exocrine tumors, that originate from exocrine cells, and endocrine tumors, that originate from endocrine cells.
Of the exocrine tumors, there are 2 types: benign adenomas (non-cancerous) and malignant adenocarcinomas (cancerous). Adenocarcinomas are much more common than adenomas, but both are rare in dogs and cats.
"Altogether, the most common pancreatic cancer in dogs and cats are insulinomas, followed by adenocarcinomas."
Of the endocrine tumors, there are 3 types: insulinomas, gastrinomas, and glucagonomas. All 3 are cancerous or malignant (i.e., invasive and prone to spread). The most common is the insulinoma, followed by the gastrinoma and the glucaconoma (see handout “Neuroendocrine Tumors” for more information on these types of tumors). These tumors are also rare in dogs and cats.
Altogether, the most common pancreatic cancer in dogs and cats are insulinomas, followed by adenocarcinomas. Both of these tumors are more common in dogs than cats.
What causes pancreatic tumors?
The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary. Insulinomas are more commonly seen in large breed dogs, such as Irish Setters, Boxers, Golden Retrievers, and German Shepherds, and also in Fox Terriers. They also appear to be more common in Siamese cats and male cats. With adenocarcinomas, Airedale Terriers may be at increased risk. Cats with diabetes mellitus may also be at increased risk. Both cancers are more common in middle-aged to older dogs and older cats.
What are the signs of pancreatic tumors?
The signs of pancreatic tumors depend on the type of tumor.
With insulinomas, the signs relate to the excessive secretion of the hormone insulin. Excessive insulin lowers the blood sugar, and low blood sugar can lead to episodes of weakness, lethargy, incoordination, mental confusion, muscle twitching, and episodes of seizures or collapse. With time, as the disease progresses, the episodes increase in frequency.
With adenocarcinomas, the signs can be vague until late in the disease process. Some pets will show signs of pancreatitis (inflammation of the pancreas). This includes loss of appetite, vomiting, lethargy, pain in the abdomen, weight loss, and sometimes yellowing of the skin (jaundice). If the tumor has metastasized (i.e., spread to other areas of the body), such as the lungs or bones, you may notice your pet has trouble breathing or lameness. Occasionally dogs will develop bone or joint inflammation. The pain from these conditions can make moving about difficult. Cats will occasionally develop hair loss on their face and along the underside of their abdomen and inner thighs.
How are these tumors diagnosed?
These tumors are typically diagnosed with bloodwork, diagnostic imaging, and exploratory surgery. Bloodwork is useful to diagnose insulinomas. It will show a low blood sugar (glucose) along with a normal or high blood insulin, as if any abnormalities are found, they are often too general to point towards the presence of a cancer.
Sometimes these tumors can be detected with abdominal radiographs, ultrasound, or CT (computerized topography) scan. If a mass is found, it may be possible to obtain a sample of the tumor cells with an ultrasound-guided fine needle aspiration (FNA). This technique uses an ultrasound probe to guide a small needle into the tumor to retrieve a sample of cells. The cells are placed on a microscope slide and examined by a veterinary pathologist. This is called cytology.
"Sometimes these tumors can be detected with abdominal radiographs, ultrasound, or CT scan."
Although cytology can be helpful, the most definitive (accurate) diagnosis of a pancreatic tumor is with a tissue biopsy taken at surgery. A tissue biopsy may be obtained by surgically removing the entire tumor or a portion of the tumor. To identify the type of cancer, the tumor or pieces of the tumor are examined by a veterinary pathologist under the microscope. This is called histopathology. Histopathology is not only helpful to make a diagnosis but can indicate how the tumor is likely to behave.
How do these tumors typically progress?
Because these tumors are malignant, they tend to metastasize, and most commonly have metastasized by the time they are diagnosed. Insulinomas metastasize most commonly to the nearby lymph nodes or the liver, although spread to any area of the body is possible. Adenocarcinomas typically spread to the nearby tissues (e.g., the small intestine) and metastasize to other areas of the body, including the lymph nodes, liver, and lungs, and less commonly other organs (e.g., bone and brain). Occasionally metastasis will cause fluid to build up in the chest or abdomen, leading to difficulty breathing or a distended (swollen) belly.
Staging (searching for potential spread to other locations in the body) is highly recommended for these tumors. This may include bloodwork, urinalysis, X-rays of the lungs, and possibly an abdominal ultrasound or CT scan. If any lymph nodes are enlarged or feel abnormal, further sampling may be pursued to determine if spread is present.
Besides spreading, as adenocarcinomas grow, they can damage the pancreatic tissue. Not only can they cause chronic pancreatitis (inflammation), but in rare cases, they can impair the gland’s ability to produce digestive enzymes, leading to a condition called exocrine pancreatic insufficiency (EPI). EPI causes chronic diarrhea with weight loss and overall poor health.
What are the treatments for these types of tumors?
Surgery to remove a portion of the pancreas (i.e., a partial pancreatectomy) is considered the best option for insulinomas. Partial removal of the pancreas leaves normal functioning tissue. Surgery is often followed by chemotherapy to suppress the spread of the tumor. When surgery is not an option, the symptoms of low blood sugar may be managed for a while with diet, the frequency of feeding, sugar supplements, steroids (hormones related to cortisol that raise blood sugar), and an oral medication that suppresses insulin secretion.
Surgery may also be attempted with adenocarcinomas. In this case, a partial pancreatectomy, complete pancreatectomy, or pancreaticoduodenectomy (removal of the pancreas and first part of the small intestine), may be considered, but because of the extensive nature of these tumors and the likelihood that most tumors will have spread (metastasized) at the time of diagnosis, surgery is often not recommended. The effectiveness of chemotherapy and radiation therapy for adenocarcinomas has so far shown little success.
Although surgery may be helpful, any surgical procedure of the pancreas risks the chance of post-operative pancreatitis, a potentially life-threatening complication.
Is there anything else I should know?
Pancreatic tumors can be difficult to diagnose, because as well as being rare, the signs of these tumors may wax and wane and are often symptomatic of many common illnesses. As they are rare, should these tumors be suspected or diagnosed, your veterinarian may refer you to a veterinary oncologist. With treatment, the prognosis for your pet may range from excellent (with the complete removal of a benign adenoma) to poor, as most of these tumors are malignant and tend to have already spread by the time they are diagnosed. Your veterinarian or veterinary oncologist will provide the information and guidance you need to make the best possible plan of care for your pet.