Histiocytoma in Dogs

These growths are common skin tumors that appear on dogs, and are usually self-healing dermal growths singular in number. They are often seen in younger dogs but do occur in canines of any age. The most common site where these growths can occur on your dog is on the head, ears and limbs. They appear as raised lumps that move freely when touched, and may become ulcerated. Most resolve themselves over time without treatment, but surgical removal is an option if it is causing a problem for your dog.

A histiocytoma is  an external buttonlike growth on your dog that is hairless or with an ulcerated surface. These are usually benign and are not painful.

• Usually a small raised button like growth that appears on the head, ears or limbs 
• Often it is a single lump but there can be more
• The lump is painless, usually hairless and the lump moves freely when touched
• When they first appear, they grow rapidly within the first 1-4 weeks
• They may become ulcerated or infected, especially if your dog starts to lick or ‘worry’ the site causing it to bleed and allowing infection to set in

Types 

There are generally two types of histiocytomas in dogs. The small button like growth is the most common, and is usually harmless, unless they become ulcerated or infected. Generally, these growths occur mostly in younger dogs and disappear over time without any treatment. 

The other variety are called fibrous histiocytomas and are not well understood. Some soft cell tumors of this type are malignant (cancerous) but they are rare in dogs. They are firm and lumpy in appearance and can be quite large. These growths require surgical treatment.

• Not a lot is known about how or what stimulates these growths but the majority seem to be harmless and self-heal given time
• Usually occurring in dogs under six years of age, and are possibly the result of growth spurts in the younger canine
• These growths are not true cancers where the cell growth is uncontrollable, but are more of an overgrowth of cells during the growing years of your pet
• No virus or infectious agent has been found to stimulate the growths, but insects such as ticks could transmit the stimulus through biting and sucking, which could be spread from dog to dog

Diagnosis depends on getting a tissue sample to be able to examine it under a microscope. This is a simple procedure that can be carried out without taking much time.

Your veterinary caregiver will use a needle or a punch biopsy to take a bit of tissue for examination. What that means is they will take a minute sample from the growth so that they can view cells under the microscope and determine the type of cell activity that is happening. The decision for treatment can then be made. 

Dogs that are most at risk from histiocytoma growths are the English Bulldogs, Scottish Terriers, Greyhounds, Boxers, Boston Terriers, and Chinese Shar Peis. If  that is your dog's breed,  be aware and have the veterinarian check them for these conditions.

Usually these growths self-heal, and if the tumor is not malignant or if it is not worrying your dog, then leaving it alone and monitoring its progress is the easiest solution. Your veterinarian will explain everything to you and will advise a regular check up to monitor the growth. 

Any ulceration needs the attention of the veterinary care giver to clean and treat the wound so that it doesn’t become worse. If infected, a medicated wash and antibiotics may be issued.

 If the growth is malignant (much less common) or is in an area where it is annoying your dog, it can be removed surgically. Your dog may need to stay in the hospital overnight and will need recovery time after surgery. In addition, if it is malignant a small area around the growth will be removed, as well as the growth itself, to ensure all the cancer has been removed. The larger and rare fibrous histiocytomas will need to be surgically removed, with the animal under anaesthetic, and stitches will be needed.

Keeping your dog from licking or biting the tumor will help prevent any inflammation or bleeding. If the area is ulcerated, taking great care to keep it clean and to stop the dog licking the growth is important. If the tumor has been removed you need to keep the site dry and clean, make sure any bandaging is kept dry, and report any swelling or bleeding to your veterinarian. Recovery is usually very quick after removal, with attention to the wound important in the first few days afterward, and a repeat visit to the clinic to assess the healing.