Adenocarcinomas in cats
© Langlais, LM et al Canadian Veterinary Journal; Wikipedia
Adenocarcinoma is a cancer that originates in glandular tissue. This tissue is also part of a larger tissue category known as epithelial tissue. Epithelial tissue includes skin, glands and a variety of other tissue that lines the cavities and organs of the body. Epithelium is derived embryologically from ectoderm, endoderm and mesoderm. To be classified as adenocarcinoma, the cells do not necessarily need to be part of a gland, as long as they have secretory properties. This form of carcinoma can occur in some higher mammals, including humans. [1] Well differentiated adenocarcinomas tend to resemble the glandular tissue that they are derived from, while poorly differentiated may not. By staining the cells from a biopsy, a pathologist will determine whether the tumour is an adenocarcinoma or some other type of cancer. Adenocarcinomas can arise in many tissues of the body due to the ubiquitous nature of glands within the body. While each gland may not be secreting the same substance, as long as there is an exocrine function to the cell, it is considered glandular and its malignant form is therefore named adenocarcinoma. Endocrine gland tumors, such as a VIPoma, an insulinoma, a pheochromocytoma, etc, are typically not referred to as adenocarcinomas, but rather, are often called neuroendocrine tumors. If the glandular tissue is abnormal, but benign, it is said to be an adenoma. Benign adenomas typically do not invade other tissue and rarely metastasize. Malignant adenocarcinomas invade other tissues and often metastasize given enough time to do so.
Pulmonary adenocarcinoma
Primary lung tumors are less common than metastatic lung lesions in dogs and cats, especially compared with their frequency in humans1. Adenocarcinomas account for 70% to 80% of primary pulmonary neoplasia in dogs and cats1; less common carcinomas include squamous cell carcinomas and adenosquamous carcinomas2,3,4. Fibrosarcomas, osteosarcomas, chondrosarcomas, hemangiosarcomas, lymphomatoid granulomatosis (angioinvasive T-cell lymphoma), histiocytic sarcoma, and adenomas are other primary neoplasms that have been documented in canine and feline lungs2.3.4.
Metastasis of primary lung tumors in dogs and cats can occur to other areas of the lungs, or to the long bones, liver, spleen, pancreas, kidneys, adrenal glands, heart, brain, oesophagus, abdominal or mediastinal lymph nodes, eyes3,5-12, or digits in cats4,7,13,14. A literature search for mention of metastasis of pulmonary carcinoma to muscle yielded only one reference14.
Most dogs and cats with pulmonary neoplasia are middle-aged or geriatric2,3. Presenting signs can include cough, exercise intolerance, dyspnea, lameness (from metastasis or hypertrophic pulmonary osteopathy, the latter more common in dogs than in cats), weight loss, anorexia, and lethargy2,3,8. Diagnosis is usually established based on radiographs, cytologic examination, and histopathologic examination.
Cats and dogs that present with firm soft tissue masses should have metastatic pulmonary neoplasia added to the list of differential diagnoses.
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Lung, cat. Neoplastic cells aggregate within pulmonary alveoli, and invade into a bronchus (white arrow) and the surrounding lung tissue (black arrows). Hematoxylin and eosin. Bar = 1000
μm.
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Skeletal muscle, cat. Neoplastic epithelial cells with prominent atypia form clusters and rare acini (white arrow) within the skeletal muscle, invading and displacing the myofibers (black
arrows). Hematoxylin and eosin. Bar = 50 μm.
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Intestinal adenocarcinoma
The most common non-haematopoietic tumour of the feline GI tract. Most occur in the jejunum and ileum, with the duodenum rarely affected. Siamese cats represented 70% of 225 reported cases of intestinal adenocarcinoma and had a mean age of 10-11 years, whereas DSH cats had the most reported cases of colonic adenocarcinoma.
Feline leukemia virus appears to have no role in the pathogenesis of this disease. Adenocarcinomas occur either as annular or intraluminal tumours. Metastasis of adenocarcinomas is typically within the abdominal cavity and not to the lungs.
Colonic adenocarcinoma
Adenocarcinoma is the most common tumour of the feline colon and most common non-haematopoietic tumour of the GI tract. It usually occurs in old cats (>10 y.o) and has higher incidence in Siamese cats. It most commonly occurs as a solitary lesion causing signs of bowel obstruction due to a large mass or annular growth around the circumference of the bowel. Malignant behaviour with metastasis to regional lymph nodes, mesentery, liver and other abdominal organs is typical of this neoplasm. However, it rarely metastasises to the lungs.
Vomiting, weight loss and anorexia are classical signs. Hematochezia, tenesmus or large bowel diarrhoea are observed the more distal the tumour location. Some cats may only have lethargy, decreased appetite or weight loss without GI signs, so history and signalment (old, Siamese cat) are important clues.
Physical examination may reveal an abdominal mass or abdominal discomfort upon palpation.
Routine haematology and biochemistry are usually within normal limits. Late changes include hypoproteinemia, hypoalbuminemia, electrolyte disturbances due to vomiting or elevations in liver enzyme activities due to metastasis. Differential diagnoses include IBD, lymphoma, other tumours or intussusception. Long-term prognosis is poor, with survival limited to 6-12 months.
Uterine adenocarcinoma
Uterine and vaginal neoplasia in cats is extremely rare in cats. Adenocarcinomas frequently involve both uterine horns, and may spread to the peritoneal cavity.