Not to be confused with the malignant histiocytosis, canine histiocytoma is the clinical term for a form of benign skin tumor found on dogs. It also can be called a button tumor. A veterinarian can biopsy the tumor to discover if it is benign or otherwise. What causes the benign tumors, however, remains unknown.
Origins of the Tumor
Histiocytoma occur on the ears, head and forelegs of dogs usually less than 5 years old. More than half were diagnosed under the age of 2. These benign tumors seem to happen spontaneously, rise quickly and in healthy dogs, may even resolve and vanish within two or three months without surgery. Evidence links these types of tumors to the autoimmune system's Langerhans cells. The Langerhans cells handle several organs that are in contact with the outside world in a dog including its stomach and nose, but most definitely the skin.
Several breeds seem more susceptible to histiocytoma growth than others. These breeds include flat-coated retrievers, bull terriers, boxers, dachshunds, cocker spaniels, Great Danes and Shetland sheepdogs. Though not officially breed-specific, the fact that this condition is more common in some breeds than in others may link histiocytoma to a genetic predisposition.
Because the tumors originate through the Langerhans cells, which in turn handle a great deal of autoimmune system work, histiocytoma may be the result of an immune system reaction. They also may be the result of the dendritic cells and histiocytes, also part of the immune system and linked to the Langerhans cells, misfiring in the way of benign tumors to develop in a similar fashion.
A histiocytoma looks similar enough visually and under the microscope to sarcoma -- cancer cells -- that a biopsy done by a veterinarian is the only way to be certain of its benign state. Though these tumors are nonpainful and fast-growing. They can become bothersome when they do not resolve themselves. Surgery to remove them is then indicated only in these cases, as a dog can live a healthy and long life otherwise.