Histiocytomas in Dogs

By Jane Meggitt

If your young dog suddenly develops a red, ulcerated lump, he might have a histiocytoma. While the overwhelming majority are benign, a small percentage of histiocytomas are malignant. Histiocytomas can resemble skin growths that are malignant, including melanomas and mast cell tumors.That's why it's important to take your dog to the vet for an examination if you find any lump on him.

Canine Histiocytomas

Histiocytomas typically appear as single, ulcerated, raised lumps. Because of their appearance, they've been dubbed "the button tumors." They originate in cells that are part of your dog's immune system, the Langerhans cells. They most often show up on the front half of the dog's body, especially the head and legs, but not always. When you palpate a lump and it slides around easily, it's probably benign -- as compared with malignant tumors, which usually don't move when palpated. Your dog might scratch at a histiocytoma, causing bleeding and secondary infection.

Affected Breeds

While any dog can develop benign histiocytomas, they appear more often in certain breeds. These include cocker spaniels, Great Danes, dachshunds, boxers, Shetland sheepdogs, bull terriers, Labrador retrievers, greyhounds, American Staffordshire bull terriers, flat-coated retrievers, bulldogs, Scottish terriers, Boston terriers and Shar-Peis. Benign histiocytoma growths generally appear in young animals, usually age 3 and under. Malignant histiocytomas most often occur in Swiss mountain dogs, Rottweilers and golden retrievers, although any dog is susceptible.

Histiocytoma Treatment

Your vet either will use fine needle aspiration to take cells from the lump, biopsy the lump, or excise the lump. No matter which method she uses, she'll then send the sample to a veterinary pathologist for diagnosis. If the tumor is benign, no further treatment is necessary, unless it is located in an area where the dog is constantly bothering it. Unlike many other forms of benign tumor, histiocytomas often disappear on their own, usually within two to three months after their appearance.

Malignant Histiocytomas

Although the overwhelming majority of histiocytomas are benign, some turn out to be cancerous. Malignant histiocytomas generally appear in middle-age canines. A skin tumor might be just a visible sign of disease that has already spread inside the body, especially the spleen, bones, kidney and liver.

Symptoms of cancerous histiocytoma include weight and appetite loss, lethargy, breathing difficulties, fever and neurological problems. If your dog is diagnosed with malignant histiocytoma, treatment consists of combination chemotherapy along with steroids. According to the National Canine Cancer Foundation, this regimen has kept affected dogs alive from several months to six years.