Round Cell Tumors

Typical cutaneous round cell tumors of dogs and cats include: histiocytoma; mast cell tumor (MCT); transmissible venereal tumor; cutaneous lymphosarcoma; other cutaneous tumors having round nuclei; melanoma; plasmacytoma and basal cell tumor.

Histiocytomas

Histiocytomas tend to occur in dogs under 3 years of age. They occur more frequently on the forelegs and head but may appear in other locations. Mast cell tumors may appear as a round raised mass, a thickened skin lesion, an open wound or a large solid mass. The mast cell tumor is often called "the great impostor" as it can appear as any lesion or non-healing wound.

Mast Cell Tumor

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. There is a general belief that mast cell tumors of the scrotum and inguinal area are more aggressive and 'malignant' than those elsewhere on the body.

The preferred treatment for a mast cell tumor confined to the upper layer of the skin with no nodal involvement is complete removal with a wide margin of at least 3 cm. If a proper margin of excision cannot be obtained, treatment usually involves surgery to remove as much of the tumor as possible followed by radiation or chemotherapy. Palliative treatment with cimetidine and histamine blockers can help prevent gastric ulceration and some of the other secondary effects of the tumor. 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).

Transmissible Venereal Tumors

Transmissible venereal tumors are frequently associated with genitalia of male and female dogs. This tumor may also be in the nasal cavity and occasionally in any area of the body in immunosuppressed dogs. They can also appear as non-healing lesions on paw pads.

Cutaneous Lymphosarcoma

Cutaneous lymphosarcoma often appears as plaque-like thickened skin or nodule. Melanomas may be distinctly pigmented or poorly pigmented. They tend to occur more frequently in the mouth. Plasmacytomas are skin tumors of plasma cells that occur on the head and limbs of dogs and cats. Basal Cell Tumors are more frequently observed on the head of dogs. The tumor may be a raised round mass resembling other round cell tumors.

Diagnosis of canine skin round cell tumors based on laboratory tests alone is often challenging. Different round cell tumors may have a similar appearance. An accurate diagnosis is important in determining prognosis and treatment.