What are round cell tumors?
Round cell tumors are among the most common skin tumors in dogs. Although they can develop in different areas of the body. They typically form just under the skin, and they may change the surface of the skin above them. Some round cell tumors are more worrisome than others.
The reason why a particular pet may develop this, or any, cancer is not straightforward. Very few cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary.
How are round cell tumors diagnosed?
Round cell tumors can only be diagnosed by analyzing tumor tissue sample under a microscope. Your veterinarian may collect a tissue sample using fine needle aspiration (FNA), which involves collecting cells from the tumor with a needle. Those cells are then analyzed by a veterinary pathologist under a microscope (cytology). If fine needle aspiration is inconclusive or not possible, your veterinarian may remove a piece of the mass (biopsy) or remove the entire tumor so the cells can be examined under a microscope (histopathology).
What are the types of round cell tumors and how are they treated?
There are several types of round cell tumors:
Mast cell tumor
Mast cell tumors (MCTs) are the most common round cell tumor in dogs. They account for 7%–21% of all skin tumors in dogs. They can occur in any breed, age, or gender, but tend to occur in older dogs and are more common in certain dog breeds (Rhodesian ridgeback, Boston terrier, boxer, pitbull terrier, Shar-Pei, and Weimaraner).
MCTs start in the skin and can spread to the internal organs if they grow aggressively, causing systemic disease. Surgery may be the only treatment needed if the tumor is found early. Tumor analysis by a pathologist will allow your veterinarian to know if additional treatment, such as chemotherapy or radiation therapy, is required.
Histiocytoma
Histiocytomas are benign tumors that tend to arise on the head, neck, legs, and feet. They are small, red, and raised, and may cause the skin surface to ulcerate (develop sores). Histiocytomas can occur in dogs of any age, but they are most common in younger dogs. They can resolve on their own, over several weeks to months, and surgery is not always necessary.
Plasmacytoma
Plasmacytomas are potentially malignant skin tumors that occur in older dogs. They appear small, raised, and red. Cocker spaniels seem to develop plasmacytomas most often. Other predisposed dog breeds include the Yorkshire terrier, boxer, West Highland white terrier, Kerry blue terrier, Scottish terrier, German shepherd, and Airedale terrier. Surgery is the treatment of choice. The vast majority of plasmacytomas are benign, but a small percentage are malignant and can progress to become a cancer called multiple myeloma.
Transmissible venereal tumor (TVT)
Transmissible venereal tumors (TVT) are sexually transmitted tumors that pass easily between breeding animals. They look like small, red, cauliflower heads. TVTs tend to occur around the genitals, nose, and mouth, and bleed if they are disturbed. Surgery may be the only treatment needed, but if the tumors recur, chemotherapy may be required.
Cutaneous lymphoma
Cutaneous lymphoma is a rare form of lymphoma, a relatively common cancer in dogs. Cutaneous lymphoma tends to occur in older dogs and generally multiple growths develop. To make a definitive diagnosis of cutaneous lymphoma, a growth must be surgically removed and analyzed by a pathologist. The pathologist’s examination will guide treatment.
What is the prognosis for round cell tumors?
Most round cell tumors are removed easily when caught early, and surgery generally resolves the issue. It is important to be vigilant and to have any skin lumps or bumps assessed by your veterinarian promptly.
