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Cancer in animals

What is Cancer?

Sadly cancer is a very common disease in older animals. It is horrible to hear that a much-loved pet has this disease but we hope that this information will help explain what is going on and that by understanding the disease, it will become less scary.

Our body is composed of many different types of cell. Each type of cell has a very different job to do and the interactions between these different cell types and the way in which they are organised allows our bodies, and those of our pets, to perform the highly complicated processes needed for everyday life.

Each cell has a finite lifespan and cells should die once they have exceeded their “best before date” to be replaced by newer cells which are constantly being produced. This ongoing “turnover” of cells within the body is tightly regulated but it can sadly sometimes go wrong. If either cells do not die when they are mean to, or cells “reproduce” too quickly, then an excess number of cells will result. These cells are not obeying the usual rules of cell division and they will continue to reproduce. This uncontrolled growth of a certain cell-type is what is meant by “cancer”.  The type of disease and clinical signs that this cancer will cause will depend on the type of cell involved. An accumulation of connective tissue cells (eg a “sarcoma”) may not cause any clinical signs other than a noticeable “lump” developing somewhere under the skin. An accumulation of insulin-producing cells (insulinoma), however, will release very high levels of insulin into the blood stream which causes blood sugar levels to plummet resulting in clinical signs of lethargy and collapse.

Not all Cancer is the same

Different cancers can therefore cause wildly different clinical signs. The behaviour of the cancer will also vary – some will stay as solitary, gradually enlarging lumps/masses whilst others can use the blood supply or the body’s drainage system to spread around the body causing secondary tumours (metastases). It is therefore important to know what type of cancer your pet has and it is sadly not usually possible to be certain from the clinical appearance (what it looks like) alone. The first stage of any investigation is therefore a biopsy procedure.

Know Your Enemy

Although some types of cancer can be diagnosed from blood tests, the majority of  cancers need a biopsy of some sort to determine what type they are. This may just be a matter of taking a few cells from a skin lump using a needle and syringe (“needle biopsy”) in a conscious animal or it may need a small surgical wound if the mass is in the deeper tissues.  Generally, the more tissue is taken, the more information is obtained but we always try to be as least invasive as possible. Your vet will help discuss any biopsies that are deemed necessary and talk you through what is involved at this stage.

Has it spread?

Once we have a diagnosis, the next question to ask is whether or not the cancer has spread. Some types of cancer never spread in which case, once diagnosed, treatment can be planned straight away. Many types of cancer, however, can spread and it is important to establish if this is the case before proceeding with treatment.  Vets often talk about the “stage” of cancer and this refers to how far a cancer has spread.  The way that we determine the stage varies depending on the type of cancer as they all have different patterns of spread through the body. Staging may involve CT scans, blood tests or further biopsies and your vet will advise you about what is involved.  Some types of cancer can have a lot more secondary disease (spread) than others and the extent of this spread will influence our recommendations for treatment.

How can it be treated?

There are many ways in which cancer can now be treated. The three main ways of treating cancer are:

  • Surgery – Cancerous masses that have not spread around the body can often be cured by surgical removal. The nature and invasiveness of this surgery will depend on the type and size of the cancer. Generally, the first attempt at surgical removal is the best chance of completely removing a cancer which is why many more complicated cancers are referred to specialist surgeons for treatment. Surgical specialists have had years of additional training in advanced techniques which enable us to safely remove and cure many cancers. What we would not want to do, however, is to put a much loved pet through a surgery if it was not going to be of any benefit to that pet. This underlies the importance of knowing the type and stage of any cancer before deciding on treatment.
  • Chemotherapy – chemotherapy uses medicine which has an effect on rapidly dividing cells. As many cancers are caused by cells multiplying too quickly and out of control, medicines which inhibit this process can also inhibit cancer. Chemotherapy may be administered by either injections (by our oncology team) or given as tablets depending on the drugs used. Chemotherapy has the advantage of targeting the whole body as, once absorbed, the drugs will be distributed to the whole body and should therefore be able to reach wherever a cancer is located whether or not it has spread. Chemotherapy does, however, have a risk of side effects including vomiting and diarrhoea, and so the dosages that we use are much lower than those used in human cases. We try to preserve your pets’ quality of life for as long as possible without exposing them to any side effects. Regular blood tests are needed to check that the body is coping with chemotherapy. The response of a cancer to chemotherapy depends on the type of cancer. Some respond very well indeed but there are some types of cancer in which the response rate to chemotherapy is so low that we do not advise this treatment.
  • Radiotherapy – Radiation can sometimes be used to kill off cancerous cells. This required highly specialized equipment and is not commonly used in veterinary medicine due to the relatively poor availability of this equipment. We do work closely with other oncology units in the UK and can arrange for your pet to be transferred to a radiotherapy unit if this treatment would be the best for your pet.
  • Combination treatments – it is common for different types of cancer to require combinations of treatments. Your pet may need surgery followed by chemotherapy in which case you will meet both the surgical oncology and medical oncology teams. We don’t want you to feel that you are being passed “from pillar to post” but we want to make sure that you are able to discuss the different phases of treatment with the specialists best qualified to answer your questions. Rest assured, we work closely together and adopt a “Team approach” (including medical specialists, surgical specialists , imagers and anaesthetists) to all of the pets entrusted to our care.


Cancer is a common disease in pet animals. Accurate diagnosis, an understanding of the typical behaviour of the cancer and checking for any secondary spread allows us to choose the best treatment for your pet and maximizes the chance of treatment success. We will help and advise you throughout the treatment process. A diagnosis of cancer is always a worry but please remember that many cancers can now be either completely cured or well controlled.