Dr. Kim Freeman, DACVIM Oncology

Is My Bernese Mountain Dog More Prone to Cancer?

As veterinarians and pet owners, we think it’s important to know if there are certain health risks associated with owning a particular breed of dog. If you start looking around, you will find that this can be the case. Why this occurs is hard to know for sure. There is some concern for over breeding and inbreeding which could lead to a narrow genetic pool, increasing the risk for disease. However, in many cases, this has not been confirmed. As veterinarians, we encourage you to speak at length with your breeder about their breeding practices and the health of their blood lines. In addition, the AKC and breed group websites (Bernese Mountain Dogs of Oregon, Bernese Mountain Dogs of America) can be very helpful.

This week, we wanted to discuss the predisposition for a cancer called histiocytic sarcoma in Bernese mountain dogs and introduce you to one of our patients, Enzo. There was a report published in 1986 that showed that in a group of 11 dogs with histiocytic sarcoma, nine of them (all Bernese mountain dogs) were related. It seems that the Berners are not alone. Other breeds that have an increased incidence of histiocytic sarcoma include flat coat retrievers, and Rottweilers. Most dogs with histiocytic sarcoma are middle aged or older, but this cancer has been reported in dogs as young as three years old.

What is histiocytic sarcoma?

Histiocytic sarcoma is an aggressive cancer of histiocytes, which are an immune system type cell. This cancer may be found in just one location in the body or can be found involving multiple organs at the time of diagnosis. Histiocytic sarcoma is the most common tumor found to affect the joints in dogs.

Symptoms of histiocytic sarcoma

There are a number of signs and symptoms that your dog might have if they have this disease. The signs greatly vary depending on where in the body the tumor is growing. If the tumor is in a joint, dogs can present with lameness. Other more nonspecific signs include lethargy, lack of appetite, and weight loss.

Diagnosis and treatment of histiocytic sarcoma

In order to diagnose histiocytic sarcoma, a biopsy orfine needle aspirate is required. In some situations, these tumors are hard to tell apart from other cancer types. There are special lab tests that are not routinely done and require a special request by a veterinarian to be done that can help with the diagnosis.

Once we have a diagnosis of histiocytic sarcoma, complete staging is recommended because this disease is often found in multiple sites throughout the body. Staging involves taking chest x-rays and having a radiologist do an abdominal ultrasound to look for evidence of spread of cancer. Although blood work is sometimes normal, often abnormalities are found on routine blood tests. A CBC tells us about the health of the bone marrow and how the cancer might be affecting the bone marrow, blood cells, and immune system. A chemistry profile can inform us about the health of the liver and whether there are other secondary metabolic problems due to histiocytic disease.

Histiocytic sarcoma, if it is already systemic, progresses quickly and is fatal if untreated. The localized form may be more slowly progressive. In one study of dogs that had anamputation for a histiocytic sarcoma affecting a joint, the average survival time was six months. However, even with amputation, most dogs eventually developed metastatic disease. Another study showed an average survival time of 391 days, for dogs with tumors located in a joint. If the tumor was not in a joint, the average survival time was 128 days.

Since histiocytic sarcoma is a cancer that spreads, we recommend chemotherapy to help slow the progression of disease or shrink tumors that are already present. We use a drug called CCNU (lomustine), which has been shown to improve the prognosis for dogs with histiocytic sarcoma. When used alone(if no surgery is done), it can help slow the cancer for about three months. When used in conjunction with radiation therapy, it has been shown to help for 19 months.

Enzo’s Story

Enzo is a 3.5 year old Bernese Mountain Dog that we are currently treating for histiocytic sarcoma. Enzo presented in October with a histiocytic sarcoma in his left stifle (knee) joint. His left knee was two to three times normal size and it was quite painful. He was on pain medications, but they just weren’t helping enough and he was getting more and more lame. Enzo had normal chest x-rays and blood work. Ultrasound showed mild enlargement of a lymph node, but it was not large enough for us to be too concerned.

Enzo visited with an orthopedic surgeon who advised against amputation. He was concerned that Enzo’s right knee might develop a ligamentous injury due to excess wear and tear, if Enzo only had one back leg. So we made a plan to help manage Enzo’s pain and cancer, without the use of surgery. Enzo was started on CCNU. Two weeks later, he started a palliative course of radiation therapy (twice a week for 3 weeks). Four weeks after startinghis treatments, he was playful and his knee felt normal! Enzo continues to do well and does not need to be on as many pain medications, due to the success of his radiation therapy and chemotherapy.

We wanted to share this success with you to help you understand that even if we can’t cure cancer, we are improving quality of life by managing it.