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What Are Dog Plasmacytomas And How Are They Treated?

While petting my Cocker Spaniel a few months ago, I felt a new, small lump on the inside of his left ear. My dog’s veterinarian performed a needle aspiration of the lump and sent the sample to a laboratory for analysis. I soon learned all about dog plasmacytomas, the official diagnosis for the 1-cm raised reddish lump on my dog’s left pinna near the external canal base. I took photos of the lump when I discovered it, in the weeks before the vet visit to monitor its progress and to show the veterinarian in followup visits.

Dog plasmacytomas, or plasma cell tumors, are round cell growths originating from lineages of B cells found in bone marrow, according to Adam Christman, DVM, MBA, Chief Veterinary Officer for dvm360. They are most commonly found in or on the skin, most specifically on a dog’s head or limbs, including the paws and between or on the toes. Dog plasmacytomas can also be located in a dog’s mouth, colon, or rectal regions. There are several types of canine plasmacytomas including benign plasma cell tumors, multiple myeloma, and single osseous plasmacytomas. The prognosis is overall very good for extramedullary plasmacytomas, and the outcome of all three types depends on the staging, location, and if there is spread or metastases of malignant cells to other areas.

In many cases, surgical removal of skin and oral plasmacytomas is curative, but others may require treatment with chemotherapy, radiation, and/or medication. “Depending on the location, size, tumor cell progress, these tumors can resolve on their own with aggressive medical therapy for 4-6 weeks and frequent rechecks with your veterinarian,” says Dr. Christman. “If surgery is warranted, a biopsy is strongly advised to confirm the diagnosis and to ensure that all tumor cells have been surgically excised accordingly.”

My dog’s plasmacytoma is the extramedullary type, and his veterinarian proposed a unique treatment plan aimed at destroying the plasma cells. I’ve interviewed other dog parents whose dogs have been diagnosed with plasmacytomas of different types and in different areas of the body. In this article, I will share all three of our dogs’ journeys, what the experts have to say, what to do if your dog is diagnosed with a plasmacytoma, and some bonus information if you find a lump or bump on your dog.

dog plasmacytomas vet visit
Dexter at the vet visit.

What Are Dog Plasmacytomas?

Most plasmacytomas are discovered on dogs by accident. Pet parents are usually petting their dog, running their fingers through his coat, examining the skin, and suddenly they feel or see a lump on the dog. There are many types of lumps and bumps that can appear on a dog, with some of them slow-growing and others progressing rapidly. Veterinarians, even the most skilled and scholarly vets, cannot tell what a lump or bump is on your dog simply by looking at it or feeling (palpating) it. Fine-needle aspiration or biopsy is required to achieve a proper diagnosis.

Dog plasmacytomas occur when plasma cells in the immune system create antibodies that work against infection or infectious diseases. A plasmacytoma results when those plasma cells are disorganized and uncontrolled.

“Most plasmacytomas are benign (not malignant),” according to Dr. Christman. “They tend to hang out near the nail beds and in between the webbing of dogs’ toes.”

dog plasmacytomas on paw
Megan Danielle’s dog with a recurrent plasmacytoma of the paw.

There are three types of dog plasmacytomas:

  1. Extramedullary plasma cell tumors: Generally found in the skin and oral cavity, such as the face, lip, and ear canals. However, they have been seen in the gastrointestinal tract, lymph nodes, and spleen. According to Kansas State University, “Oral plasmacytomas are biologically more aggressive than cutaneous counterparts and can undergo local invasion into the underlying bone, however a complete surgical excision of the mass results in only rare recurrence or metastasis.” They are generally solitary and do not spread. Dr. Christman reports they are generally benign but only a biopsy of some sort can confirm that.
  2. Multiple myeloma: This type of plasmacytoma is usually a very malignant cancer. It may involve several organs and bones and cause pain to the dog. Dogs with multiple myeloma may have a certain type of protein in their urine. Without treatment, such as chemotherapy, and sometimes radiation, multiple myeloma can be fatal.
  3. Solitary osseous plasmacytoma: Though rare, they can affect any bone in the dog’s body. Long Island Vet Specialists say most dogs with a solitary osseous plasmacytoma will advance to multiple myeloma.

Once a dog is diagnosed with a plasmacytoma and the type is known, I would most definitely seek a veterinary oncologist for a solitary osseous plasmacytoma, multiple myeloma, or extramedullary plasma cell tumor (depending on its location). It’s always a good idea to ensure the plasmacytoma is confined to a single location in the dog’s body.

What Are The Symptoms Of A Canine Plasmacytoma?

Most dog plasmacytomas that are diagnosed as extramedullary are found by the pet parent through palpation or seeing a new lump or bump on or in the dog’s skin or somewhere on his body. The mass is generally raised, red or pink, 1 to 2 centimeters at first, and may bleed.

For the more aggressive type of plasmacytoma, multiple myeloma, the Veterinary Information Network lists symptoms of fatigue, vomiting, loose stools, and lack of appetite. However, many other diseases and conditions may cause the same symptoms, which is why aspiration or biopsy of a lump is imperative for a proper and early diagnosis.

Solitary osseous plasmacytomas in dogs arise from bone. Thus, lameness and pain are potential symptoms. Diagnostic testing is imperative and a bone marrow aspiration, biopsy, radiographs, blood work, or other lab tests are usually performed on the dog.

Is A Canine Plasmacytoma A Type Of Cancer?

Plasmacytomas contain plasma cells and they can multiple and become abnormal and malignant. Not all plasmacytomas are cancer, as is the case with an extramedullary plasmacytoma. Dr. Christman says most plasmacytomas are benign, and the National Canine Cancer Foundation agrees, as multiple myeloma accounts for less than 1 percent of neoplasms in all animals.

“Dr. Christman says most plasmacytomas are benign, and the National Canine Cancer Foundation agrees, as multiple myeloma accounts for less than 1 percent of neoplasms in all animals.

— Adam Christman, DVM, MBA

Yes, plasmacytomas are a type of canine cancer but in most cases, Dr. Christman and other experts agree they are benign. If the cancer is advanced or spread to other organs, an oncologist should most definitely be involved in the dog’s care.

dog plasmacytomas on ear
Dexter’s ear before CryoProbe, left, and several weeks after

What Are The Common Places Canine Plasmacytomas Appear?

Extramedullary dog plasmacytomas occur in places like the skin or mucous membranes, including a dog’s mouth, gums, and lips. If the plasma cells are found in the bone marrow, this would be considered a medullary plasmacytoma.

“They tend to hang out near the nail beds and in between the webbing of dogs’ toes,” Dr. Christman notes. “In regions that don’t involve skin, this type of tumor can be found inside the dog’s mouth and colon regions.   Most of these tumors are solitary and less than one percent are associated with multiple myeloma (plasmacytoma arising IN the bone marrow).”

My 12-year-old Cocker Spaniel’s plasmacytoma showed up on his ear pinna near the external ear canal. Susan Thaw Greenberg’s dog, 10-year-old Woody, was diagnosed with a plasmacytoma in his mouth located between two of his lower jawline teeth. Megan Danielle’s 12-year-old dog had surgery for a plasmacytoma on the bottom of her foot. A few months later, it grew back to almost twice the size and further intervention is needed.

Woody with Dr. Liptak

Are Certain Dog Breeds More Prone To Plasmacytomas Than Others?

Although any dog can be affected by plasmacytomas, Dr. Christman says certain breeds are at greater risk. These include West Highland Terriers, Golden Retrievers, Labrador Retrievers, Standard Poodles and Cocker Spaniels.

Extramedullary plasmacytomas comprise about 2.5 percent of all neoplasms in dogs and occur most commonly in middle-aged to older dogs (mean 8 to 10 years). Over at dvm360, they mention Boxers and Airedale Terriers as additional breeds of extramedullary plasmacytoma. Solitary osseous plasmacytomas (SOP) are rarely reported in dogs and most cases progress to multiple myeloma months to years after local tumor development.

How Are Dog Plasmacytomas Diagnosed?

Cytology and immunochemistry are the two most commonly used tools for diagnosis and staging. Cytology involves cell analysis and immunochemistry uses antibodies to look for certain markers in a tissue sample.

If surgery is warranted, Dr. Christman says a biopsy is strongly advisable to confirm the diagnosis and to ensure that all tumor cells have been surgically excised accordingly.

Susan Greenberg’s Cocker Spaniel, Woody, had a biopsy to confirm the diagnosis of extramedullary plasmacytoma. Susan took a photo of Woody and noticed a red spot on his gums. After the diagnosis, Dr. Joseph Cyrus, an internal medicine specialist, aspirated Woody’s liver and spleen to be sure it had not spread throughout his lymphatic system. The aspirates were clean, his one enlarged lymph node was aspirated, it came back normal, and Woody did not have multiple myeloma.

Susan has peace of mind knowing the surgical margins are clean. If the margins around the plasmacytoma were not clean, further surgery would be required, as the cells could become malignant. Because Woody’s plasmacytoma was in his mouth, surgical removal was recommended.

Because my dog’s extramedullary plasmacytoma was located on his ear, his vet performed a fine-needle aspirate in the office and sent the samples out for laboratory diagnostics. She also gave him a shot of Benedryl in the event the lump was a mast cell tumor, as that would help calm the irritated lump. Dexter’s cytology report is shown below. Surgical excision was recommended.

diagnosis of dog plasmacytomas

In Dexter’s case, and with his history of a previous autoimmune disorder (IMT) and a mitral valve disease, our vet suggested we do cryosurgery using super-cooled liquid nitrogen. Our veterinarian reminded us the ear has many blood vessels and Dexter would require general anesthesia for complete removal and to properly control bleeding. We discussed options and agreed on CryoProbe.

CrypoProbe was used during a subsequent visit after my dog received a local anesthetic to his ear. Cryotherapy is an excellent option for dogs who have certain types of lesions. I wanted to avoid general anesthesia, so we opted for freezing the lump. He was done in 15 minutes and there were no adverse side effects. Although our vet told us two CryoProbe sessions may be necessary, we stopped after one treatment.

The lump was frozen and, in the weeks, after, dead tissue slowly sloughed off. I kept it clean and had to apply an antibiotic powder to the area when it bled a bit. After a month, it didn’t seem to decrease in size and the vet felt a second treatment would not be effective. We talked about having it removed via laser surgery under twilight anesthesia in the future, but since that time, the lump has decreased significantly.

Cryotherapy has been shown to reduce the size of the growth (again, pending on location) but doesn’t necessarily completely remove the margins, according to Dr. Christman. This may be beneficial to pet parents with financial constraints for surgery and prepare a multimodal approach to therapy, including cryotherapy and medications. Due to the dead tissue sloughing off and entering Dexter’s ear canal, he developed an inner ear infection in the affected ear.

During a followup visit, we were prescribed antibiotic ointment. After 10 days of antibiotic and increasing my dog’s CBD oil, the lump suddenly decreased significantly.

dog plasmacytomas after treatment
The plasmacytoma in Dexter’s ear is almost gone.

What Is The Treatment For Canine Plasmacytomas?

Treatment for dog plasmacytomas varies. Sometimes, cryotherapy can be used. Dr. Christman reports they may not always need to be removed, as he has had personal success with canine clients using corticosteroids and an antibiotic, doxycycline. He says depending on the location, size, and tumor cell progress, these tumors can resolve on their own with aggressive medical therapy for four to six weeks and frequent rechecks with your veterinarian.

Surgery may involve traditional excision under general anesthesia, the use of twilight anesthesia for local excision, cryotherapy, or laser surgery for extramedullary plasmacytomas of the skin.

In Woody’s case, Dr. Julius Liptak, an oncology surgeon and surgical specialist in small animal surgery, recommended a mini mandibulectomy, an operation for benign or low-grade oral tumors of the mouth. A small wedge was removed, which included the mass and two incisor teeth.

Preoperative and postoperative photos of dogs who underwent a unilateral rostral mandibulectomy can be seen here, with images of Woody’s pre- and postoperative photos below. The Merck Veterinary Manual reports when this type of tumor arises in the mouth, it tends to multiply.

dog plasmacytomas in mouth
Woody preoperatively.
dog postoperatively for removal of plasmacytomas
Woody postoperatively.

For solitary extramedullary dog plasmacytomas, dvm360 reports complete surgical removal is often curative. They say non-oral extramedullary plasmacytomas are more aggressive in behavior and dogs are often treated with surgery alone or surgery with additional therapies, such as medicine, chemotherapy, and/or radiation.

Dogs with more aggressive multiple myeloma should be under the care of a veterinary oncologist to discuss treatment options including, but not limited to, surgery, radiation, chemotherapy, and medication(s).

More Information On Canine Lumps And Bumps

I’ve been through most lumps and bumps on dogs over the past few decades, and I’ve learned a lot. Like people, no two dogs are alike and no two lumps are the same. Here are few articles I’ve written to help guide you in your knowledge of lumps and bumps on dogs.

Dog Parent Guide To Lumps On A Dog

Unexpected Warning Signs Of Dog Cancer

How To Treat And Prevent Lipomas In Dogs

Help For Dogs With Mast Cell Tumors

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Has your dog ever been diagnosed with a plasmacytoma? Tell us in the comments below.

How are dog plasmacytomas treated

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4 Comments

  1. Thank you! This article explained a lot to me about my dogs condition and options for treatment. I greatly appreciate the time you take to share this information with your readers.

  2. what was the final outcome from the dog that had it on his paw? that is what we are currently dealing with.

    1. We haven’t received any updates from her owner, but a plasmacytoma in that location most definitely needs to be removed. I would 100 percent see a specialist/oncologist or qualified surgical veterinarian for this.

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