Types of Tumors

Mast cell tumors

Mast cell tumors are the #1 skin tumor of dogs and are composed of cells that typically involved in the allergic response. As such, mast cell tumors are known to secrete certain substances that can cause swelling, redness, bleeding and even stomach ulcers. Mast cell tumors are readily diagnosed by fine needle aspiration and may range in biological behavior from very malignant to benign. Assessment of malignant potential (grading) is only possible after biopsy is obtained. Thus, current recommendations involve removal of mast cell tumors with 2 cm lateral margins of normal tissue and a deep plane of muscle underlying the skin tumor. Since surgical removal of mast cell tumors can involve removal of large amounts of skin, special reconstructive skin flaps or grafts may be required to close the defect during surgery.

Perianal tumors

(tumors occurring in the skin around the anus) Due to difficulty in removing large areas of skin around the anus, tumors in this region are typically sampled prior to complete removal. Perianal tumors in male dogs tend to be hormone related and can be cured by mass removal and neutering. In female dogs, tumors of the anal sac (apocrine gland adenocarcinoma) can be highly malignant. These tumors may be treated by aggressive local removal after evaluation of the local lymph nodes (in the abdomen). Enlarged lymph nodes may also be removed from the abdomen, although prognosis for long term survival is guarded. Perianal tumors can produce a substance that causes elevated levels of calcium in the blood, another marker that can be used as a prognostic indicator after surgical removal.

Splenic tumors

The spleen is an organ located in the abdomen that is involved in immune function and production/storage of red blood cells. Splenic tumors are most commonly encountered in older, large breed dogs, but can occur in any breed of dog or cat. Approximately 50% of splenic tumors are malignant (can spread to the rest of the body) and it is important to perform a complete diagnostic evaluation including chest x-rays and abdominal ultrasound or CT scan to search for evidence of other tumors. Certain types of splenic tumors are prone to rupture, causing bleeding into the abdomen and associated clinical signs such as weakness, pale gums, and distention of the abdomen. Other tumors are detected incidentally during annual physical examination or during screening ultrasound of the abdomen. Definitive diagnosis and therapy is most commonly achieved by removal of the spleen (splenectomy), as the spleen is not an essential organ in the dog or cat. Some dogs require preoperative blood transfusion if they have experienced significant bleeding from the tumor. Long term prognosis is dependent upon the tumor type as determined by biopsy results.

Osteosarcoma

The most common type of bone tumor seen in dogs is osteosarcoma. Typical clinical signs include a progressive lameness (limp) in an older, large breed dog in association with a swelling or pain in a long bone. Certain breeds appear to have a genetic predisposition for development of osteosarcoma , including the Irish wolfhound, Rottweiler, and retriever breeds. The radiographic appearance of mixed bone destruction and excessive bone production in a succeptible breed is highly suggestive of this diagnosis, but suspicious areas can be confirmed by a needle biopsy performed under a brief anesthetic. Chest x-rays or computerized tomography (CT s can) are required to assess for metastasis (spread of the tumor) to the lungs. Bone cancer is typically malignant and is rarely cured by surgical therapy. Thus, therapy is directed at two goals: 1) pain relief by surgical removal of the bone tumor and 2) slowing the spread of the tumor by administering chemotherapy. The most common palliative surgery performed in dogs with bone cancer affecting one of the leg bones is amputation of the affected limb. Although many pet owners are hesitant to perform amputation surgery on their dogs, postoperative surveys show that 80-90% of people are happy that they made the decision and would do so again, if required in future pets. For dogs with concurrent orthopedic or neurologic problems that would make them poor candidates for amputation surgery, various “limb sparing” te chniques are available, which involve local removal of the affected bone and replacement with various metallic or bone implants. Radiation therapy may also be used to control pain and local tumor growth. Survival statistics for dogs with osteosarcoma is well described and averages approximately 5 months without chemotherapy and 12 months with chemotherapy. Dogs will typically develop evidence of heavy breathing or coughing as metastasis of tumors occurs in the lungs. Dogs that do not receive pain relieving surgery can be treated with various analgesic drugs, but these drugs have limited efficacy and owners will often decide that quality of life is not acceptable after several weeks. Weakening of the bone in the location of the tumor may also predispose to pathologic fracture, causing sudden increase in discomfort and difficulties with medical management.