Pancreatic Neoplasms in Small Animals
Neoplasias of the exocrine pancreas can be primary or secondary and can be classified as benign or malignant. Most exocrine pancreatic neoplasias in dogs and cats are secondary.
Pancreatic adenomas are benign tumors that are usually singular and can be differentiated from pancreatic nodular hyperplasia by the presence of a capsule. Pancreatic adenocarcinoma is the most common primary neoplastic condition of the exocrine pancreas in dogs and cats but is rare overall in both species.
Benign neoplasms of the exocrine pancreas can lead to transposition of organs of the cranial abdominal cavity. However, these changes are subclinical in most cases, and the diagnosis is often made as an incidental finding during necropsy. In rare cases, the neoplastic growth can obstruct the pancreatic duct and cause secondary atrophy of the remaining exocrine pancreas, leading to exocrine pancreatic insufficiency. Adenocarcinomas may lead to tumor necrosis if the tumor outgrows its blood supply. Tumor necrosis causes local inflammation, which can lead to clinical signs of pancreatitis. Malignant neoplasms may also spread to neighboring or distant organs.
The presentation of dogs and cats with exocrine pancreatic neoplasia is nonspecific, and many cases remain subclinical until late in the disease process. Some animals show clinical signs suggestive of pancreatitis. Obstructive jaundice may be seen if bile duct obstruction develops. Clinical signs related to metastatic lesions have also been reported in some cases of pancreatic adenocarcinoma and may present as lameness, bone pain, or dyspnea. Finally, paraneoplastic alopecia has been reported in cats with pancreatic adenocarcinoma.
Several nonspecific findings, such as neutrophilia, anemia, hypokalemia, bilirubinemia, azotemia, hyperglycemia, and increased hepatic enzyme activities, have been reported in dogs and cats with pancreatic adenocarcinoma. However, results of routine blood tests may be unremarkable. Increased serum lipase and amylase activities and trypsin-like immunoreactivity and pancreatic lipase immunoreactivity concentrations have not been commonly reported in either dogs or cats with pancreatic adenocarcinoma but may be seen in either species.
Radiographic findings are also nonspecific in most cases. Abnormal findings include decreased contrast in the cranial abdomen suggesting peritoneal effusion, transposition of the spleen caudally, and shadowing in the pyloric region. In some cases, abdominal radiographs suggest a cranial abdominal mass. Abdominal ultrasonography generally shows a soft-tissue mass near the pancreas, but in many cases, continuation of the mass with pancreatic tissue cannot be conclusively demonstrated. Also, neoplastic lesions of neighboring organs may be falsely presumed to be of pancreatic origin. Finally, animals with severe pancreatitis may show a mass effect in the area of the pancreas on abdominal ultrasonography that must not be confused with a pancreatic neoplasia.
If peritoneal effusion is present, a sample should be aspirated and evaluated cytologically. However, in most cases neoplastic cells do not readily exfoliate into the peritoneal effusion, and no neoplastic cells are identified on cytology. Fine-needle aspiration or transcutaneous biopsy under ultrasonographic guidance can be attempted when suspicious masses are identified. However, in many cases, the diagnosis is made at exploratory laparotomy or necropsy.
Pancreatic adenomas are benign and theoretically do not require therapy unless they cause clinical signs due to the effects of an intra-abdominal space-occupying lesion. However, because the final diagnosis of pancreatic adenocarcinoma is often made at exploratory laparotomy, a partial pancreatectomy should be performed even in cases of suspected pancreatic adenoma. The prognosis in these cases is excellent. Animals with pancreatic adenocarcinomas often present at a late stage of the disease, and metastatic disease at the time of diagnosis is quite common in both dogs and cats. Common sites for metastasis are the liver, abdominal and thoracic lymph nodes, mesentery, intestines, and the lungs, but other metastatic sites have also been reported. In those few cases when gross metastatic lesions are not identified at the time of diagnosis, surgical resection of the tumor may be attempted, but clean surgical margins can almost never be achieved, and owners should be forewarned. Both chemotherapy and radiation therapy have shown little success in human or veterinary patients with pancreatic adenocarcinomas. Thus, the prognosis for dogs and cats with pancreatic adenocarcinoma is grave.