Cutaneous Histiocytoma in Dogs

By Krista Williams, BSc, DVM, CCRP; Malcolm Weir, DVM, MSc, MPH; Joan Rest, BVSc, PhD, MRCPath, MRCVS

What are histiocyte cells and what do they do?

The histiocyte group of cells is part of the body's immune surveillance system. They take up and process foreign antigens, such as pollen and microorganisms (viral, bacterial, and fungal).

They then migrate to the local lymph nodes where they present the antigens to other immune system cells (T lymphocytes) to stimulate them into a variety of activities to protect the body. The cells that are involved in cutaneous histiocytoma are called Langerhans cells.

What is a cutaneous histiocytoma?

A cutaneous histiocytoma (not to be confused with histiocytosis) is a common, harmless (benign) tumor of Langerhans cells. In the tumor’s early stages, over the first one to four weeks, the cells grow rapidly. During this rapid growth, they often ulcerate and may become infected. Later, they may regress spontaneously.

What do we know about the cause?

Very little is known about the cause of histiocytomas. The reason why a particular dog may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary. Most dogs that develop cutaneous histiocytomas are young, and spontaneous self-cure is common with time.

Are cutaneous histiocytomas common?

This is a common tumor. Most affected dogs are less than three years old, but this tumor can occur at any age. The tumor can occur in any breed, but some breeds appear to be more susceptible to the tumor, including boxers, Great Danes, and dachshunds.

How will this tumor affect my dog?

The most obvious effect of this tumor is the lump. Many will regress spontaneously over a few months. Although there is a risk of secondary infection and bleeding, these tumors are often left to regress. If infection, ulceration, or bleeding can’t be treated of if the tumour doesn’t shrink within one to two months, then your veterinarian may recommend surgical removal.

Occasionally, the local lymph nodes may swell. This swelling may be a reaction to secondary infection; however, it could also indicate spread of the abnormal cells to the lymph node or a different diagnosis. Any changes in lymph node size should be re-assessed by your veterinarian.

It is unusual for more than one tumor to be present on the same dog or for the same tumor to occur later at another site. If this happens, it may indicate another condition called cutaneous Langerhans Cell Histiocytoma: a rare disease in which histiocytomas spread (metastasize) to other sites in the skin, the lymph nodes, or even internal organs. This disease is more common in Shar Peis.

How is this tumor diagnosed?

Clinically, this tumor has a button-like appearance – a red and/or ulcerated bump. Accurate diagnosis relies upon microscopic examination of tissue. Depending on the location, your veterinarian may recommend one or more methods of obtaining a tissue sample for diagnosis. The most common methods include needle aspiration, punch biopsy, and full excision biopsy (removing the growth).

"Accurate diagnosis relies upon microscopic examination of tissue."

The sample will then be examined by either cytology or histopathology. Cytology is the microscopic examination of aspirated cell samples, and is used for rapid or preliminary assessment. Histopathology is the microscopic examination of tissue and is used for more accurate diagnosis, prediction of behavior (prognosis), and to determine whether a tumor has been fully removed. This test is done at a specialized laboratory by a veterinary pathologist. Your veterinarian may submit a small part of the mass (biopsy) or the whole lump (an excision biopsy). If your veterinarian performed an excision biopsy, the pathologist also assesses whether the cancer has been completely removed.

What treatment is available?

This tumor is one of the rare types that the dog’s own immune system can eliminate. However, ulceration, itching, secondary infection, and bleeding may often require intervention, including topical or systemic antibiotics or surgical removal.

In most cases, surgical removal is a permanent cure. Your veterinarian may recommend sending the tumor to a pathologist to confirm it is a cutaneous histiocytoma and that it has been completely removed (i.e., there are no microscopic cells remaining in the surrounding, apparently normal tissue).

How can I care for my dog with a cutaneous histiocytoma?

Prevent your dog from scratching, licking, or biting the tumor to reduce itching, inflammation, ulceration, infection, and bleeding. Any ulcerated area needs to be kept clean.

If the mass is removed surgically, keep the incision site clean and dry and prevent your pet from rubbing, licking, biting, or scratching at it. Report any loss of sutures or significant swelling or bleeding to your veterinarian. If you require additional advice on post-surgical care, consult your veterinarian.

Are there any risks to my family or other pets?

There are no reports of tumors spreading between animals.

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