Cancer of the Blood Vessel Cells in Dogs

Hemangiopericytoma is a skin tumor that is believed to form on the pericyte cells that surround the cutaneous blood vessels. Pericyte cells are undifferentiated embryonic cells; they are neither blood vessel nor muscle tissue, but they could develop into either. This is one of many closely related tumors that form in the connective skin tissue on dogs. It’s not always entirely clear which connective cells form the tumor, so these types of tumors may be given a number of different names, including spindle-cell sarcoma, neurofibrosarcoma, or peripheral nerve sheath tumors. Some veterinarians will distinguish between the tumors based on individual cell type, while others will evaluate them as a group. Hemangiopericytomas are most identifiable by the concentric circles or fingerprint pattern that forms on the tumor; however this feature may not be present in all cases. The tumors are found commonly on the legs in older or middle aged dogs. They are usually a discrete lump, but in some cases they can ulcerate, bleed, and become infected. This is a cancerous neoplasia, however, it rarely metastasizes beyond the skin. It will continue to grow and, if left untreated, can become very large. Surgical removal is the best treatment, but the tumors often infiltrate the surrounding cells microscopically and it can be difficult to remove all the cancerous tissue. For this reason, recurrence is often a problem. Bleeding can sometimes be a concern with removing larger tumors.

In older dogs, skin tumors in the cells that support the blood vessels can be quite common. Veterinarians define this condition as hemangiopericytoma. The tumors are malignant, but they rarely spread beyond the skin and are therefore less serious than other types of cancer.

Hemangiopericytoma does not usually cause pain for the dog unless it is located in an area where it puts pressure on other organs. If you notice an unusual lump on your dog, it should always be evaluated by a veterinarian. These features could indicate hemangiopericytoma.

• A nodular tumor on the limbs or thorax
• Tumor may be pinkish, or bald, often with whorls spreading out from the center
• Bleeding or infected tumor

Types

Hemangiopericytomas are divided into two types, based on their rate of metastasis.

• Low grade – this type of tumor spreads slowly and there is only a 25% rate of recurrence
• High grade – this type of tumor is more aggressive and has a 62% chance or coming back after surgery; the most malignant tumors could also spread internally to other parts of the body, but this is rare

Microscopic tissue analysis will be needed to determine what type of tumor your dogs has.

There is no known cause for this or any other type of cancer. There may be a number of contributing factors, including, diet, hormone levels, and radiation or injuries sustained throughout a lifetime. The following conditions suggest a higher likelihood.

• Age – tumors are much more common in older dogs
• Sex – this type of cancer seems to be more common in female dogs
• Breed – it is more common among larger dogs. Some breeds have a greater risk
• Mixed breed dogs
• Siberian Huskies
• Irish Settlers
• German Shepherds

The veterinarian may suspect hemangiopericytoma based on the appearance of the tumor, but microscopic analysis will be necessary to make a definitive diagnosis. Tissue samples are often taken with fine needle aspiration or biopsy. In some cases, the tumor may not be fully analyzed until it is removed with surgery. 

Biopsy and cell analysis will help the veterinarian check for other, potentially more serious, types of cancer, especially hemangiosarcoma. This is another type of blood vessel cell cancer that is often found internally on the spleen. The skin version has a similar prognosis to hemangiopericytoma, unless the tumor is subcutaneous in which case it can spread internally and cause more serious systemic problems.

The veterinarian will want to know your dog’s complete medical history, age and breed. Bloodwork may be done to check coagulation levels since bleeding can be a problem during biopsy or surgery. The veterinarian will also evaluate your dog’s overall health to determine if he is a good candidate for surgery.

If the veterinarian determines that the tumor is removable and your dog is healthy enough for surgery, this is the best treatment. The veterinarian will need to remove a margin of healthy cells along with the tumor to help ensure it doesn’t return. The area will be bandaged after surgery. You will need to check the incision and keep it clean. Antibiotics may be prescribed to limit infection.

Most tumor removal is minor surgery. In some cases, however, an entire limb might need to be amputated if the tumor itself can’t be easily removed. This happens most commonly with very large tumors or tumors that have returned after surgery. When tumors regenerate, they are often much more deeply rooted and difficult to remove. Amputation isn’t usually necessary with a small, first-time tumor.

The veterinarian may recommend radiation or chemotherapy treatment after surgery, especially if the tumor was diagnosed as high grade. Hemangiopericytoma does not respond to well to chemotherapy, but small, frequent, doses can sometimes help to avoid recurrence. Radiation is more effective, but also considerably more costly. Your dog will likely need to spend a number of weeks in a veterinary hospital to manage the side effects. Radiation may also be prescribed if the tumor is deemed inoperable.

Dogs with removable, low-grade tumors have a good chance of making a complete recovery. The median survival time for dogs with these types of tumors is 2-4 years. High-grade tumors have a much lower survival time of 49 weeks, but these types of tumor are less common. Whatever the prognosis you should examine the area for signs of recurrence and schedule frequent check-up’s so the veterinarian can monitor your dog.

Recurrent or inoperable tumors may eventually require euthanasia since if they grow too large they will put pressure on vital organs. Other health issues that complicate surgery or limit the length of your dog’s life usually play a factor in this choice.