Common Tumors Of The Cat And Their Management

 Dennis W. Macy DVM, MS
Colorado State University, Fort Collins, Colorado 80523

 

Tumors of the skin and subcutaneous tissues

Skin tumors of the cat account for 20% of feline tumors.  Squamous cell car­cinomas (SCC) of the skin of cats usually develop in nonpigmented, sparsely-haired areas of the cat.  The ear tips, nose and eyelids are frequent areas of SCC development in the cat.  Squamous cell carcinoma is usually preceded by preneoplastic skin changes charac­terized by crusting and erythema and skin erosions.  Fortunately, these ultravio­let-induced neoplasms are of low grade, slow growing, and seldom metastasize.  Super­ficial SCC may be managed with cryosurgery, hyperthermia, or irradiation.  Invasive SCC requires an aggressive surgical approach.  Invasive SCC of the nasal planum may be treated with nosectomy with 70% of patients being tumor free at one year.  Palliative therapy may include intralesional injections of carboplatin.

Mast cell tumors are the second most common tumor of the skin in the cat.  Two or perhaps three types of mast cell tumors occur in the skin of cats.  The most common are those that share similar histopathologic characteristics as canine mast cell tumors but can also be subdivided into compact and diffuse types.  A second less common mast cell tumor are his­tiocytic mast cell tumors with morphologic features characteris­tic of histiocytic mast cells.  A possible third type is a miliary mast cell tumors of the skin of cats.  Siamese are predisposed to the first two types of mast cell tumor.

The most common types of mast cell tumors in the cat are low grade and don't require as wide of surgical margins as their canine counterpart.  However, surgical removal is still associated with a 19-24% recurrence rate.  Histiocytic mast cell tumors occur in young Siamese cats and undergo spontaneous regression in 4-24 months.  The miliary form of mast disease is unusually unresponsive to corticosteroid treatment.

Fibrosarcomas are the most common sarcomas and the fourth most common tumor of the skin and subcutaneous tissues of the cat.  Although the etiology of the vast majority of fibrosarcomas of the cat are unknown, the fibrosarcoma virus and vac­cination and/or other causes of chronic inflammation have been identified for some fibrosarcoma in cats.  Virally-induced fibrosarcoma is caused by the feline fibrosar­coma virus and is a rare form of fibrosarcoma that may be multicentric and frequently affects young cats.  Since 1991, fibrosarcoma and other soft tissue sarcomas are known to develop after the administration of inactivated vaccines (rabies and FeLV).  Virally induced and vaccine-associated tumors are usually high grade and are more aggressive than those FSA not associated with these two etiologies.  The local recurrence follow surgical excision of all forms of feline FSA range from 40-70%.  Radiotherapy is only moderately effective in controlling fibrosarcomas and is best used when treating micros­copic disease.  Chemo­therapy Adriamycin, vincristine and carboplatin have all shown effectiveness in the palliative setting in the management of vaccine-associated fibrosar­coma in the cat.

Adenocarcinoma of the intestinal tract

Adenocarcinoma of the feline intestine is usually at an advanced stage at the time of diagnosis.  Extension of the neoplasm beyond the bowel wall is not uncommon.  IN one study in 32 cats, 71% had gross histologic evidence of metastasis at the time of diagnosis.

In another report, 123 cats with small intestinal adenocarcinomas were treated with intestinal resection and end-to-end anastomosis.  Of the 12 cats that survived the perioperative period, the average survival was 15 months following surgery.  Five of these cats were staged as extending beyond the primary site to regional lymph nodes.  The five cats with known lymph node metastases had a mean survival time of 12 months.  The bottom line is that metastatic disease of the intestinal tract is not neces­sarily associated with a poor prognosis.  In human recurrence, it can be reduced 37% with levanisol.  The recommended levanisol dosage is 3 mg/kg every other day for one year postoperatively.  For cats with gross evidence of metastasis, mitoxantrone is given every three weeks at a dose of 6.5 mg/m2.

Osteosarcoma

Osteosarcoma in cats has many similarities to the same disease in dogs, but some important differences exist.  The histologic type, radiographic appearance, and location have similarities to the same disease in the canidae.  Despite this fact, pul­monary metastasis is much less common in the cat.  IN one study involving cats undergoing amputation for osteosarcoma of the appendicular  skeleton, the median survival was greater than 48 months.  In the cat, osteosarcoma of the axial skeleton does not have as good a prognosis as osteosarcoma of the distal extremity.

Feline mammary neoplasia

Feline mammary neoplasia is of paramount importance to the veterinarian because 80 to 90% are considered malignant, with adenocarcinoma being the predominate histologic type.  This must clearly be differentiated from fibroepithelial hyperplasia.  Fibro­epithelial hyperplasia usually occurs in young, cycling, pregnant female cats, even in those before their first estrus.  This condition is frequently confused with either malignant neoplasia or mastitis.  Some have recommended ovariohysterectomy to resolve the problem.  However, other have identified that this will resolve on its own.  The most significant prognostic fact affecting recurrence and survival for feline malignant mammary tumors is tumor size.  Cats with tumors greater than 3 cm in diameter have a median survival time of 6 months.  Cats with tumors 2 to 3 cm in diameter have a median survival of about 2 years, and cats with tumors less than 2 cm in diameter have a median survival of about 3 years after surgery.  Radical mastectomy is currently the most recommended treatment of choice.  Mitoxantrone and/or Adria­mycin/cyclophos­phamide chemotherapy may be of benefit for increasing the disease-free interval.  Histologic grading may be an important prognostic variable.

RESPIRATORY

Nasal tumors

The most common nasal tumor in the cats is a nasal adenocarcinoma.  Lymphoma is less common, but it is an important clinical entity.  Radiation therapy, with or without surgical rhinotomy, often results in long-term control of nasal tumors in cats.  In those cats with localized nasal lymphoma, radiation therapy, with or without chemotherapy, may be of great value.  In one report, the mean and median survival of these cats was 123 and 113 weeks, respectively.

Thymomas occur in the thoracic cavity of older cats and produce similar clinical signs as cats with thymic lymphosarcoma.  Thymomas originate from thymic epithelium and are infiltrated with mature lymphocyte populations.  Clinically "benign" and invasive "malignant" thymomas have been described in the cat.

A thymoma is a surgical disease while thymic lymphosarcomas are best treated with chemotherapy thus the two must be differentiated.  Eighty percent of the lym­phomas in the chest are FeLV positive and fine needle aspiration usually yield lym­phoblasts.  Fine needle aspirations of thymomas may yield small lymphocytes but seldom yield to neoplastic epithelial component.  Trial treatment with vincristine or Adriamycin have also been used in making a therapeutic diagnosis.  Fifty percent of the thymomas are resected surgically.  Reported median survival of two years have been reported.

Oral cavity

The two most common oral neoplasms in the cat are SCC (70%) and fibrosarcomas (20%).  Squamous cell carcinoma have a predilection for the mandible, maxilla and tongue while fibrosarcoma frequently occur on gingiva in the cat.  Lymph node metastasis is only occasionally seen with either tumor.  Bone involvement, however, is a frequent sequelae.  Both SCC or FSA of the oral cavity are considered radioresistant and the primary treatment should be aggressive surgical excision.  The prognosis of oral SCC is very poor while oral fibrosarcoma is fair.  Unique tumors in cats include inductive firbroameloblastoma which is a rare odontogenic tumor affecting young cats under two years of age.  The tumor occurs in the maxilla and is characterized by varying degrees of bone destruction, production and expansion of the maxillary bone.  Another tumor type found as young cats is the nasopharyngeal polyp.  Clinical signs often include sneezing, difficulty breathing or swallowing.  These tumor-like lesions are made of fibrous connective tissue and originate from the middle ear and grown down the eustachian tube into the pharynx to appear as pedunculated masses.  Surgical removal with or without bullae osteotomy is the treatment of choice.

Tumors of stomach and intestine

The stomach is the least common site of the intestine for tumors in the cat.  The most common histology is the lymphoma, which is best treated with chemotherapy.  The most common tumors of the intestine of cats is LSA, adenocarcinoma and MCT.

Most intestinal tumors occur in older cats and Siamese account for 70% of the reported adenocarcinomas of the small intestine in cats.  LSA of intestine of the cat is usually FeLV negative.  Most adenocarcinomas present as advanced disease with more than 70% having evidence of metastasis at the time of diagnosis; transcoelomic metas­tasis is common.

Treatment - LSA of the intestine is associated with approximately six months survival.  Despite the high metastatic rate of adenocarcinoma of small intestine; the mean survival time of one year following local resection has been reported.