Last week, after discussing the benign haemangiomas (HAS), I promised to continue with haematomas – all within the context of the surface tumours theme. However, we’ll have to postpone the conversation on haematomas, since one revered colleague from overseas reminded me that there is another haemangioma condition which I should write about. He was referring to haemangiosarcomas which, unlike other cancers, is pretty much exclusive to dogs. I must thank him for his observation. I had omitted this ailment, because one does not often see it in Guyana. Actually, I found more interest in the fact that our column is being read by erstwhile Guyanese vets who are not practising at home. Now let’s have a look at HAS.
The haemangiosarcoma is different from what we discussed last week in that it is quite lethal. This is indeed a mysterious and challenging disease. First of all, it is an incurable tumour of cells that line blood vessels. Secondly, it seems to affect only dogs – and, in the USA, many of them at that. A paper by veterinary doctors Modiano and Pitt estimates that this type of cancer accounts for 5-7% of all tumours seen in dogs in America. Considering the lifetime risk of cancer in dogs is between1 in 2 and 1 in 3, we can calculate that 1.5 to 2.5 million of the 72 million pet dogs in the United States today will get haemangiosarcoma and succumb to it. Although dogs of any age and breed are susceptible to haemangiosarcoma, the statistics reveal that HAS occurs more commonly in big dogs beyond middle age (older than 8 years), and in breeds such as Golden Retrievers, German Shepherds, Portuguese Water Dogs, Bernese Mountain Dogs and Flat Coated Retrievers.
(I should mention quickly in passing that a similar type of tumour occurs in humans, but only rarely and mostly in association with workplace exposure to certain chemicals (such as those found in rubber/tyre plants). Therefore, we here in Guyana, ought not to worry too much about this type of cancer.))
Haemangiosarcoma is known as a silent killer because it usually develops slowly and painlessly until it reaches an advanced stage. The disease can occur as a single tumour within one major organ or multiple tumours throughout the body. Unfortunately advanced staged tumours seem resistant to most treatments. And they are usually advanced before the dog owner recognizes a problem and brings his/her companion animal into the vet’s clinic. The standard-of-care for this tumour is surgery and intensive chemotherapy. HAS cases occur most commonly in those large breed dogs mentioned above when they are eight to ten years of age.
So, those were some general comments about HAS. But what causes haemangiosarcomas?
The scientists do not precisely know the aetiology (cause) of canine haemangiosarcomas. The observations that the disease occurs more commonly in dogs than in other animals, and that some breeds are at higher risk than others tell us that heritable factors must contribute to the exhibition of this disease. Ultimately, the interactions of these heritable risk factors with the environment probably lead to the spectrum of cell mutations that give rise to the tumour. These mutations provide cells a selective growth advantage within their environment, essentially the same evolutionary phenomenon that we call natural selection, albeit on a microscopic scale.
Having re-read what I have just written, it is clear that my own excitement about the ‘science’ behind this disease has gotten the better of me – and the fact that I have gone into such detail might not find favour with the most of this column’s readers. Sorry!
So, let’s get back on track.
Symptoms of HAS
Signs can range from subtle to overt, and may include unexplained weakness, nosebleeds, pale mucous membranes, abdominal swelling and depression. Some animals just collapse and sudden death follows.
Haemangiosarcomas can cause extremely large tumours – 10 pounds or more. Therefore, veterinarians often locate these large tumours upon physical examination of the abdomen. I remember, as a young assistant in my university’s policlinic, being confronted with an HAS in the spleen of a beautiful Golden Retriever. That cancerous growth weighed in at just under 4kg. Tumours affecting other organs, such as the heart, can be very small and difficult to diagnose, often requiring X-rays, lab tests and exploratory surgery. Veterinarians may also aspirate fluid from the abdomen. But in the end, we usually don’t win.
The prognosis for dogs with a haemangiosarcoma depends on a number of factors, such as size of the tumour and location. But let’s face the facts: the prognosis for haemangiosarcoma is very poor. Death is usually the outcome. I might add that a common estimate of the average time from discovery of the (haemangiosarcoma) tumour until death occurs in affected dogs is six to eight weeks. Of course, death occurs more rapidly when the tumour spreads quickly (metastasis).
Let us conclude today’s TPC on this morbid note.
Next week we’ll assuredly write about haematomas.