Extramedullary Plasmacytoma in Dogs

Cocker spaniels are one breed with a predisposition for extramedullary plasmacytomas.
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Extramedullary plasmacytomas, also known as mucocutaneous plasmacytomas, are fast growing tumors that originate in the plasma cells. With no known cause, these tumors are generally found on the trunk, legs, feet, rectum, mouth and ears. While these tumors are typically benign in nature, they account for 2.5 percent of all canine neoplasms. According to a 2012 paper published in the "Journal of Veterinary Medicine," 22 to 28 percent of all extramedullary plasmacytomas occur in the mouth. The good news is surgical tumor removal is typically successful and the prognosis is good.

What Do Plasmacytomas Look Like?

Extramedullary plasmacytomas appear as smooth, red raised lumps on the skin. If the tumor develops in the mouth or lips, oral bleeding may occur. These types of tumors are solitary in nature, meaning you will likely only see one. Occasionally, these tumors occur in the colon or rectum, causing rectal bleeding, maroon-colored stool, bowel movement discomfort and difficulty and rectal prolapse.

Certain Breeds Have a Higher Risk

Extramedullary plasmacytomas typically occur in middle-aged dogs, with the median age being between 9 and 10 years, according to the National Canine Cancer Foundation. While they can occur in any breed, certain breeds are predisposed. These breeds include cocker spaniels and West Highland terriers.

How the Veterinarian Diagnoses Plasmacytomas

If you notice an abnormal growth on your dog, seek veterinary care as soon as possible. Your veterinarian will need to determine what type of growth it is, as well as rule out multiple myelomas. Possible diagnostic tests will include blood work, urinalysis, tissue biopsies or fine-needle aspirations, bone marrow aspirations, lymph node aspirations and possible X-rays, depending on the location of the tumor.

What Kind of Treatment Will My Dog Undergo?

Because these tumors typically do not metastasize, surgical removal is often enough. In areas on the skin and mouth, or internal tumors, where complete removal is not possible, radiation therapy or chemotherapy may be necessary. In cases of large growths on the feet, amputation may be the only option to remove the tumor. If complete removal of the tumor is possible, the cure rate is typically between 90 and 95 percent, making the prognosis very high.