PET HEALTH CARE ARTICLES

Primary liver tumors in dogs and cats are rare. There are 4 types: hepatocellular tumors, bile duct tumors, neuroendocrine tumors, and sarcomas. These cancers can be massive, nodular, or diffuse in form. In dogs, most liver tumors are malignant, while in cats, most are benign. The signs of liver tumors range from being asymptomatic to having inappetence, fever, lethargy, and weight loss; and less commonly, nausea, vomiting and diarrhea; increased drinking and urination; and jaundice. Occasionally there are neurological signs, such as seizures. With tumor rupture and intrabdominal bleeding there may be weakness, collapse, and difficulty breathing. The diagnosis is based on history, clinical signs, exam findings, diagnostic imaging, and FNA or liver biopsy. A biopsy is best for a definitive diagnosis. Surgery is the treatment of choice for most primary liver tumors followed by chemotherapy. Chemoembolization is a newer treatment.

Intestinal tumors are uncommon in dogs and cats, comprising about 2% of all cancers. There are many kinds, including leiomyosarcomas, lymphomas, adenocarcinomas, mast cell tumors, gastrointestinal stromal tumors (GISTs), plasmacytomas, carcinoids, and osteosarcomas (all malignant) and leiomyomas, adenomatous polyps, and adenomas (all benign). Most intestinal tumors are malignant. Intestinal tumors are more prevalent in older animals and certain breeds. Signs, diagnosis, and treatment are discussed.

Primary intraocular tumors, aside from melanoma, are relatively uncommon. There are many different types of primary tumors, including ciliary body adenoma and adenocarcinomas, uveal schwannomas of blue-eyed dogs, feline post-traumatic ocular sarcomas, and iridociliary adenomas and adenocarcinomas. When an intraocular tumor is suspected, a referral to a veterinary ophthalmologist may be recommended. Diagnosis is usually via an abnormal ophthalmic examination and/or ophthalmic ultrasound. Surgery is often recommended, especially if the pet has symptoms that reduce quality of life. The risk of metastasis is related to the type of tumor.

There are a number of tumors that affect the eyelids, conjunctiva, and periocular tissues. These can be benign or malignant and can lead to secondary problems such as eye infections and corneal ulcerations. Diagnosis is best achieved through complete surgical excision of the tumor, but fine needle aspiration may be pursued as an initial diagnostic. Surgery is highly recommended to provide the pet with symptomatic relief, remove the tumor, and obtain a definitive diagnosis. With malignant tumors, surgery is the mainstay of therapy, though radiation therapy is sometimes pursued in cases where surgical removal is not possible.

Eye melanomas in cats may be benign or malignant (cancerous). Malignant tumors, called diffuse iris melanomas, show up as multiple spots of color change in the iris, while benign tumors, called limbal melanomas, present as a distinct mass at the edge of the cornea. The diagnosis of these tumors is largely by clinical signs and tumor appearance. Treatment for diffuse iris melanomas may include close monitoring, laser surgery, removing part of the iris (iridectomy) and removing the eye (enucleation). Metastasis has been reported in about 19-70% of cases of diffuse iris melanoma, with most spread to the regional lymph nodes, kidneys, liver, and lungs. Treatment for limbal melanomas may include close monitoring, and surgery, sometimes combined with cryosurgery, laser surgery, or radiation therapy. Enucleation is an option if the treatment is unsuccessful, or the tumor regrows.

Esophageal tumors are extremely rare but more often than not malignant type tumors. The cause is unknown but cases in tropical environments may be due to infection by the worm Spirocerca lupi. Treatment options are limited as surgical complications are high due to the advanced nature of the disease at time of diagnosis.

Collecting tissue samples for cytology or histopathology allow a pathologist to often give a diagnosis of the type of mass or tumor your pet has. Samples can be obtained by fine needle aspirate or biopsy, where a piece of the mass is cut out. Based on what the mass appears like under the microscope, the pathologist can often give a prognosis of how the tumor will behave.

A chemodectoma is a type of tumor made up of chemoreceptor cells. Chemoreceptor cells detect chemical changes in the body and respond by regulating chemical or physical processes. These tumors are most often seen along one of the carotid arteries and the aorta. Brachycephalic breeds are more predisposed to these types of tumors, though they may occur in any dog breed. These tumors are usually locally aggressive, however, there are rare cases of metastasis to other organs, including the lungs, lymph nodes, and bone.

Chondrosarcomas arise from cartilage, which is a connective tissue primarily found where bones meet with joints, as well as at other locations in the body such as the nasal cavity, and ribs. Chondrosarcoma is a rare tumor in cats, but it can occur. Clinical signs of chondrosarcoma may vary significantly, depending on where the tumor arises. Although the mass may grow rapidly, less than 20% of feline chondrosarcoma cases metastasize to other parts of the body. Therefore, surgical removal is curative in many cases.

Skin cancers are common in cats, but cutaneous lymphoma is relatively uncommon. Less than 2% of lymphoma cases in cats occur in the skin. As the disease progresses, the skin becomes thickened, reddened, ulcerated, and may ooze fluid. The most common locations to find lesions include the junction between mucus membranes and the skin. Unfortunately, feline cutaneous lymphoma is considered incurable. Surgical removal can be attempted for solitary lesions, although the tumor often returns to the area or will have spread elsewhere in the body already