Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Dr Liesel van der Merwe

May is pet cancer awareness month. Cancer is becoming more common in our pets as they are living longer due to improved care and nutrition as well as preventative management of disease. Veterinarians are learning more every day in how to diagnose these conditions.

To a large extent animals present with the same tumours found in humans and the characteristics are also very similar. However, the detailed sub-classifications of the various tumours is not available in animals as less is generally know and case numbers undergoing treatment are less than in people.

Cancer is generally more common in older animals but some forms have a predilection for younger animals as well. In the majority of situations we do not know what causes cancer. Some, such as skin cancer, are obviously related to lack of pigmentation and sun exposure, being common on the ear tips and nose of white cats and the tummy of white dogs (fox terriers, bull terriers and Staffordshire terriers being common).

You may see an obvious lump developing in or under the skin, or you may take your dog or cat to the vet for a seemingly unrelated symptom and be confronted with a diagnosis of cancer. It is important to realise that not all cancers (malignancies or neoplasia being synonyms) are equal. Some grow slowly and do not really spread to other organs. These cancers are classified as having a more benign behaviour.

Cancers with malignant behaviours can either be very rapid growing and invasive at their initial site or they may spread rapidly to other organs, such as the lungs, liver and spleen. Tumours will initially spread to the local glands, which in proper terms are called lymph nodes. The progression of cancer is more rapid in our pets than in humans, as their lifespan is shorter.

The first responsibility of the veterinarian once he suspects a tumour is to try to identify the kind of cancer and also to see how big it is and how far it has spread. This process is called staging and each kind of tumour has different criteria by which this classification is made. The prognosis and best treatment option depend on how the tumour is staged and this allows both you and your veterinarian to make an informed decision on whether to treat or euthanize your pet, and which treatment protocol is likely to give the best results.

In some situations surgical removal of the tumour is all that is required, in others only chemotherapy or radiation therapy is required, and some will require surgical removal as well as additional therapies.
The aim in many treatment situations is remission, not cure. Some low-grade chemotherapy protocols aim only to prevent further progress of the cancer and not treat that which is already there.

Chemotherapy conjures up awful images for most owners as they have seen people undergo treatment. Veterinarians will use many of the same drugs used in humans to treat pets, but the dosages are lower and the regimens less intense. In general there are very few side effects to chemotherapy in veterinary patients. Sometimes patients are a little nauseous for a day or two after treatment, but more serious side effects are extremely rare.

Owners who elect chemotherapy have to be emotionally prepared to live with the ever-present threat of progression of disease and also have to be dedicated to vet visits for treatments and check-ups for blood counts and other monitoring requirements.

The aim should be to prolong life if possible without causing any suffering or pain and in some situations where cancer is diagnosed this may be possible.

Common cancers
Mammary tumours: Sterilisation before the second heat (even before the first heat) dramatically decreases the incidence. Approximately half of the tumours are very malignant.

Lymphoma (gland cancer): It is amenable to treatment with good remission rates in many cases.

Squamous cell carcinoma (skin cancer): This is a locally recurrent, invasive sun-induced cancer. Treatment includes surgical resection, local chemotherapy and radiation.

Osteosarcoma (bone cancer): It is common in large breed dogs and is very painful and malignant, needing amputation and chemotherapy.

Haemangiosarcoma (splenic tumour): It is especially common in German Shepherd dogs. There is no really effective treatment, but removal of the spleen is palliative for about three to six months.

Mast cell tumours: These skin nodules range from benign to very malignant and can present under many guises.