Extramedullary Plasmacytomas in Dogs

Diagnosis and Treatment of These Types of Tumors

Dog at the vet's
Cocker spaniel being examined at the vet's. Getty Images/Vstock LLC

Plasmacytomas are tumors that arise out of a specific type of white blood cell called plasma cells. There are several types of plasmacytomas that arise in different parts of the body:

  • extramedullary plasmacytoma -- in soft tissue outside the bone marrow, for example, in the skin. Relatively common in dogs, but rare in cats.
  • multiple myeloma -- plasma cell neoplasia within the bone marrow. A complex and serious disease, though fairly rare in dogs and cats.
  • single osseus plasmacytoma -- arise from the bone. Also rare in dogs in cats. Often progresses to multiple myeloma eventually.

Among extramedullary plasmacytomas, there is further variation depending on where these plasmacytomas are found. On the whole, extramedullary plasmacytomas do not tend to be very aggressive tumors and usually have a good prognosis. Extramedullary plasmacytomas can be found in these locations:

  • Skin: by far, the most common location for extramedullary plasmacytomas. Studies estimate that 75-86 percent of extramedullary plasmacytomas are found in the skin. They are often found on the head, especially the ear, and the extremities.
  • Oral Cavity: studies estimate that 9-25 percent of extramedullary plasmacytomas occur in the mouth or on the lips. These can be somewhat invasive where they occur but do not tend to spread to other locations.
  • Other Sites: it is estimated that around 4 percent of extramedullary plasmacytomas occur in the colon or rectum, while 1 percent occur in other locations such as the stomach, small intestine, spleen, genitals, eye, etc. These types tend to be a bit more serious than the skin or oral forms, but still usually respond quite well to treatment.

    Risk Factors of Certain Breeds

    Extramedullary plasmacytomas are most often seen in older animals. Cocker Spaniels, Airedales, Scottish terriers, West Highland White Terriers, Yorkshire Terriers, Boxers, Golden Retrievers, and Standard Poodles may have a greater risk of developing plasmacytomas.

    Signs and Symptoms of Plasmacytomas

    With the skin and oral types, there are usually no clinical signs other than the tumor itself.

    Characteristics of plasmacytomas include:

    • raised pink or red mass
    • small, often only 1-2 cm in diameter but sometimes grow larger
    • sometimes multiple tumors will grow, especially in the oral cavity
    • occasionally bleed a bit and may become ulcerated

    When the plasmacytomas arise elsewhere, they can sometimes produce variable signs related to their location and size (e.g., straining to defecate for tumors in the rectum, difficulty breathing if in an airway, etc.).

    Diagnosis of Plasmacytomas

    Extramedullary plasmacytomas can be diagnosed by microscopic examination of a sample of cells taken from the tumor with a needle (called a fine needle aspirate) or biopsy (usually of the tumor itself after removal). After a tumor is removed surgically, the edges of the tumor can also be examined microscopically to determine if the entire tumor was removed successfully.

    Lymph nodes around the tumor may also be checked to make sure tumor cells aren't spreading. Very rarely, extramedullary plasmacytomas are associated with multiple myeloma, so your vet may run tests to rule out this more serious illness, especially when dogs with plasmacytomas have unexplained clinical signs or are generally unwell.

    Treating Plasmacytomas

    In general, the prognosis is good for extramedullary plasmacytomas.

    They can cause problems locally, but usually do not spread to other locations, with some exceptions.

    For skin and oral plasmacytomas, completely removing the tumor surgically is usually sufficient to cure the tumor. Occasionally, tumors will regrow; in these cases, surgery can be repeated and radiation or chemotherapy considered as well. Radiation and/or chemotherapy can also be considered in cases where surgical removal is difficult, if multiple tumors are present, or if there is evidence that tumor cells have spread beyond the tumor.

    Though plasmacytomas in other soft tissues -- not the skin or mouth -- tend to be more aggressive and sometimes spread, these also respond relatively well to surgery or surgery with additional treatment such as chemotherapy.

    More About Dog Health

    Please note: this article has been provided for informational purposes only. If your pet is showing any signs of illness, please consult a veterinarian as quickly as possible.