Round Cell Tumors

Dogs and cats can be affected by a variety of skin tumors. Cells from round cell tumors are small, individualized, and round. Typical skin round cell tumors are: histiocytoma, mast cell tumor, transmissible venereal tumor, cutaneous lymphosarcoma, melanoma, plasmacytoma, basal cell tumor, and other skin tumors having round nuclei. Some tumors are more aggressive than others. For instance, tumors of the nasal cavity and paranasal sinuses in dogs account for only approximately 1% of all neoplasia; however, over 80% are malignant. Tumors can cause chronic blood loss leading to iron deficiency anemia.2 Different round cell tumors may have a similar appearance and diagnosis of canine skin round cell tumors is often a challenge. In addition, some round cell tumors are more aggressive and carry poor prognosis. However, timely testing can save a dog's life.

Histiocytomas typically occur on the forelegs and head and tend to affect dogs under 3 years of age. Mast cell tumors (MCT) are one of the most common canine skin tumors. The mast cell tumor is often called "the great impostor," as it can appear as any lesion or a non-healing wound. Although the Boxer and Golden Retriever seem to be predisposed, MCT can develop in dogs of any breed, with middle-aged to older dogs having a higher risk. There is a general belief that mast cell tumors of the scrotum and inguinal area are more aggressive than those elsewhere on the body. The preferred treatment for mast cell tumors is complete removal with a wide margin of at least 3 cm, followed by radiation or chemotherapy.

Old dogs are predisposed to round cell tumors
Old dogs are predisposed to round cell tumors

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 provides very good results with low toxicity. A recent development in the treatment of must cell tumors is the introduction of a new class of drugs that act differently from chemotherapy. Whereas chemotherapeutic drugs work by directly damaging a cell's genetic material, these new drugs interfere with the body's messaging system that controls the division and proliferation of cells. In addition, these drugs can be given orally. Toceranib phosphate (Palladia) is beginning to be widely used by veterinarians not just for the treatment of mast cell tumors, but also several other cancers.1

Transmissible venereal tumors are frequently associated with genitalia of male and female dogs, although in immunosuppressed dogs they may involve the nasal cavity, paw pads, and other areas of the body. Cutaneous lymphosarcoma often appears as plaque-like thickened skin or nodule. Melanomas may be distinctly pigmented or poorly pigmented and tend to occur more frequently in the mouth. Plasmacytomas are skin tumors of plasma cells affecting the head and limbs of both dogs and cats. Basal cell tumors, frequently observed on the head of dogs, may look like a raised, hairless, firm, round mass resembling other round cell tumors. Most basal cell tumors are benign, grow slowly, and may develop for years before diagnosis. The treatment of choice for these tumors is surgical removal, which has a good prognosis.3


  1. Lawrence Lindner, Nicholas H. Dodman (editor). Good Old Dog: Expert Advice for Keeping Your Aging Dog Happy, Healthy, and Comfortable
  2. Iron deficiency anemia
  3. Textbook of Small Animal Surgery, Volume 1. Douglas H. Slatter (editors)
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