Canine Cancer Information

Soft Tissue Sarcomas
Soft tissue sarcomas (STSs) consist of a variety of tumors that arise from mesenchymal cells. Tumors included in this group are fibrosarcomas, peripheral nerve sheath tumors, and hemangiopericytomas. They typically appear as firm, subcutaneous (under the skin) masses, which may be located on the extremities, trunk, or head and neck. They usually are slow-growing tumors, but may also come up quite quickly. These tumors are locally invasive, and are not likely to go to other sites (metastasize).

Diagnosis involves either cytological (fine needle aspirate) or histopathological (biopsy) evaluation. If your dog is diagnosed with a STS, the primary treatment recommendation is surgical removal of the mass. The feasibility of surgery will depend on the size and the location of the tumor. Because these tumors can be invasive, diagnostic tests such as a CT scan may help to identify the extent of the mass. We also may need to do other diagnostic tests such as thoracic (chest) radiographs prior to surgery to look for metastases. We also consult with the Surgical Service to get their opinion on the surgical options, to discuss potential complications of surgery, and to get an estimate for the surgical costs. Once the mass has been removed, histopathological evaluation offers additional information about the potential aggressiveness of the tumor, referred to as the histological grade. If the tumor appears to be aggressive, then other treatment modalities such as chemotherapy, may be recommended to prevent its recurrence or metastases. In addition, histopathological evaluation helps to determine if the tumor was completely excised. If the tumor was not completely excised, then post-operative radiation therapy or chemotherapy may be beneficial in preventing local recurrence.

As you may have noticed, there are many variables to consider. We will do our best at discussing the tumor type that your dog has, the treatment options that are available, the prognosis, and the cost associated with treatment.

Canine Mammary Tumors
Mammary tumors are extremely common in dogs; approximately 50% of them are malignant. Mammary tumors are more common in intact than in spayed females; in fact spaying before the first or second heat cycle significantly reduces the risk of developing mammary tumors. Median age on presentation is 10 to 11 years. Dogs fed a high-fat diet or overweight at 1 year age are at increase risk of developing mammary tumors. Appropriate early treatment, even if the tumor is malignant, is often curative.

If you are petting your dog and you notice a lump along the mammary chain, please have your vet examine her. In intact female dogs you may notice lumps that come and go after the heat cycle; they are typically due to mammary gland hyperplasia (proliferation of normal mammary tissue).

Before any diagnostic or therapeutic steps are taken, the health status of the dog must be fully assessed. Bloodwork and urinalysis should be done to identify any presurgical abnormalities. Thoracic radiographs (both right and left lateral and ventrodorsal planes) should be obtained to search for pulmonary metastases. A fine needle aspiration cytology of the mass is usually not recommended because its diagnostic value to discern between malignant or benign tumors is very low. Regional lymph nodes (lymph glands) should be palpated carefully; fine-needle aspiration or surgical removal are necessary to determine the presence of metastases.

Unfortunately the only way to know if mammary tumors are benign or malignant is to surgically remove them and do a biopsy. It doesn't matter how many mammary tumors a dog has: because all of them can be different, every mass should be submitted to the lab and analyzed. Depending of the size and the number of tumors conservative surgery (lumpectomy/ single mastectomy) or a more aggressive surgery with removal of a whole mammary chain may be recommended.
As of now, there is no proven efficacy of any chemotherapeutic protocol for the treatment of malignant mammary tumors in the dog. Certain drugs used for the treatment of carcinomas or sarcomas like gemcitabine/carboplatin/ doxorubicin may be helpful in delaying recurrence or metastases, but their efficacy is unknown.
The prognosis for dogs with malignant mammary tumors depends on the following factors: tumor type, size, regional lymph node (lymph gland) involvement, presence or absence of distant metastases, completeness of resection, local behavior, vascular or lymphatic invasion, and tumor differentiation.

As a general rule with this type of cancer, the best prognosis is directly related to early detection and treatment.

Canine Lymphoma
Lymphoma (lymphosarcoma, LSA) is a cancer of the lymphocytes (white blood cells) most commonly originating in the lymph nodes (lymph glands), although it may affect any organ, including spleen, liver, intestines, and skin. Fortunately, most (~90%) patients treated with combination chemotherapy undergo clinical remission (no visible evidence of cancer) for extended periods of time.

During your appointment with The Ohio State University Veterinary Teaching Hospital Oncology/ Hematology Service, your dog's previous history and diagnostic findings will be reviewed. In most cases, fine-needle aspiration cytology will be done to assist in confirming the diagnosis, particularly if a previous biopsy is not available. A tissue biopsy (usually done under sedation with a slightly larger needle) often also is obtained to confirm the cytologic diagnosis and to provide additional information. Additional diagnostic procedures may be required, including abdominal ultrasound, thoracic radiographs, bone marrow aspirate, urinalysis, and blood samples for a complete blood count (CBC) and serum chemistry profile. All of this information assists in making a diagnosis of lymphoma, and assessing the extent of disease and suitability for treatment.

Lymphoma in most instances is a very chemotherapy responsive disease. For most patients, chemotherapy using a combination of drugs is recommended. During the "induction phase" of chemotherapy, patients receive intravenous injections of drugs on a weekly basis as well as some oral drugs at home. After completion of induction therapy, some patients will continue to receive maintenance therapy consisting of oral drugs alone, or in combination with intravenous drugs. On average, about half of treated patients live over one year beyond the initiation of chemotherapy and 20% for longer than 2 years. Some treatments (ie. UW-19 protocol) uses chemotherapy for only a limited period of time (ie. 19 weeks).

Chemotherapy is well-tolerated by most dogs. Possible side-effects include nausea, vomiting, diarrhea, inappetence, and myelosuppression (low blood cell counts), but is self-limiting in most instances. Hospitalization due to chemotherapy-related complications is rare (~5-7%). Quality of life for dogs with lymphoma on chemotherapy, as judged by the owners, usually is excellent.

Mast Cell Tumors
Mast cell tumors (MCTs) are one of the most common skin tumors in dogs. Although some breeds are predisposed, such as Boxers and Golden Retrievers, MCTs can develop in dogs of any breed. Middle-aged to older dogs have a higher risk of developing MCTs, but young dogs can also be affected.

Mast cell tumors can resemble almost any lesion of the skin or subcutaneous tissue, such as erythematous (red) areas, nodules (bumps), masses (lumps), benign or malignant skin tumors (lipomas, hemangiopericytomas, etc), so a cytologic evaluation (needle aspirate) of any cutaneous or subcutaneous lesion is always indicated. Cytologically, MCTs consist in a population of round cells with intracytoplasmic purple granules. Although the behavior of MCTs is unpredictable without treatment, the histologic (microscopic) grade is helpful in establishing their behavior; thus a histopathology study (biopsy) has to be performed in all cases. Microscopically, MCTs are graded as well-, moderately, and poorly differentiated (grades 1, 2, and 3, respectively).

In general, well-differentiated (grade 1) MCTs have a low metastatic (ability to spread) potential, while moderately- and poorly-differentiated MCTs have a higher metastatic potential to regional or distant lymph nodes (lymph glands), spleen, liver, bone marrow, and other organs.

The clinical evaluation of a dog with a MCT includes physical examination, a complete blood cell count, biochemical profile, urinalysis, fine needle aspirate from the lesions or affected sites for cytology evaluation, abdominal ultrasonography, and, sometimes, thoracic radiography if thoracic lymphadenopathy is suspected.
The treatment is variable depending on the histopathologic grade and extent of disease; complete surgical excision is frequently curative in dogs with solitary grade 1 or 2 MCTs. When surgical excision is incomplete (there is evidence of tumor cells at the surgical site) 3 options are available: to perform another surgery immediately,if possible, or to use radiation therapy or chemotherapy.

When MCTs can't be surgically removed, radiation therapy is recommended, although in some cases chemotherapy may have similar effects. In dogs with grade 3 MCTs or with metastatic MCTs, chemotherapy is the treatment of choice. In general a combination of lomustine (CCNU) and prednisone provide very good results with low toxicity (side effects).

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Soft Tissue Sarcomas

Canine Mammary Tumors

Canine Lymphoma

Mast Cell Tumors

ATTENTION:
Those with herding breeds (Collie, Sheltie, Border Collie, Corgi, etc).
There is a genetic defect that runs in many lines of herding dogs. It is important to test for this (MDR1) in order to determine if your dog can tolerate chemotherapy.

The test can be administered by your vet through a blood test (must be sent out for results) or a cheek swab that you can administer at home.

Additional information, test instructions
and forms can be found here.
 

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