Cancer in our pets

Our pets suffer from some of the same diseases as humans, and sadly cancer is one of them. A diagnosis of cancer can be a worrying time, but constant advances in the field of Oncology (the study of cancer and its treatments) mean we can do a lot to help.

The first rule of oncology - check every lump early - is the best life saver of all.

What is cancer?   Normal body cells live and die to a pattern and these cells grow and divide in a controlled way. Tumour cells have lost the natural pattern of ageing and dying, and no longer respond to the state of their neighbours in the control of their growth and division. When these changes are relatively minor a benign tumour, composed of relatively normal cells which keep together in a lump, will develop, pushing normal cells away but not pushing between them, or invading blood and lymphatic vessels. Malignant cells have not only lost the control on life span and division rates but, to a degree which varies between tumours, also grow between surrounding cells to spread amongst normal tissue and to invade blood and lymphatic vessels. Tumours which invade blood and lymphatic vessels can escape the area of the primary tumour, and travel to the next narrow vessels (usually the lungs or liver if via blood or the local lymph gland if via lymph). Here they can grow into new secondary (or metastatic) tumours.

Diagnosing Cancer

  • Examination - visual examination of a lump, along with feel, can yield clues as to its nature. A full examination of the patient for other lumps and/or complications which may be associated with certain tumours is a first step in the diagnostic process.
  • Fine needle biopsy and cytology - insertion of a fine needle into the lump can allow cells to be removed and placed on a slide for examination. Whilst some tumours cannot be diagnosed by this method, a significant number can be identified, and sometimes their degree of malignancy can be assessed. A simple and quick stain may give a definite diagnosis in some tumours.
  • Solid biopsy and pathology - the definitive diagnosis of a tumour is carried out on a solid piece of tissue removed under anaesthetic, either before an attempt is made to remove the tumour, or at definitive surgery. This is sent to a laboratory for examination.
  • X-ray - one of the main ways to look inside a body to obtain information about disease. Many pets with cancers will have their chests X-rayed to check for the presence of secondary tumours in the lungs. However the cells or clumps of cells that spread to the chest are microscopic, so an X-ray can only detect well establish tumours.
  • Ultrasound & MRI - ultrasound allows us to see tumours which would not be detected by X-ray. The images obtained by MRI are immensely detailed and can be very useful in planning treatment of tumours.
  • Exploratory surgery - there are times when none of the above methods will give enough information and we have to use surgical exploration to assess a tumour. Generally this will be combined with an attempt to remove the tumour, or at least to obtain biopsy specimens.
  • Staging - this is the assessment of local, regional and distant spread of the tumour, and of complicating factors, if any. Staging can give a good idea of the chance of success of surgery or of other treatments. It is the sum result of all the investigations described above.

Treating Cancer

The first essential in cancer treatment is the pet's quality of life. Pain-free, functional and dignified life is the aim. Any temporary detrimental effects of treatment, whether surgery, chemotherapy or other, must be minimised and be justified by the subsequent improvement in the pet's quality of life.

Any treatment can have side-effects, but every effort is made to minimise or eliminate these. Surgery to remove a tumour may cause some post-operative pain, but modern pain killers are very effective and most pets will appear comfortable during recovery.

Different treatments have different abilities to get rid of cancer cells. There are some cancers which are only treated by chemotherapy (e.g. lymphomas). Otherwise surgery is the first line of attack, radio- and chemo-therapy are next in being able to destroy large tumours.

  • Surgery - the most effective treatment by far for almost all tumours is surgery. If done early and effectively it can cure a large proportion of tumours which would otherwise become life-threatening. Surgery to remove a tumour will involve the removal of some normal tissue around the tumour. Samples are sent to the laboratory after surgery and checked for adequacy of removal.
  • Chemotherapy & Radiotherapy - chemotherapy has a reputation (in humans) for causing nasty side-effects. It is usual for chemotherapy in pets to be less aggressive than in humans, so side-effects are reduced. If a pet suffers significant side-effects with chemotherapy, the dose rates can be modified or other drugs could be tried. The main method of using radiation to destroy cancer cells is when the radiation is produced by a machine and beamed into the body aimed at the tumour.
  • Palliative therapy - in some cases there is no reasonable possibility of getting the disease under control. In these cases palliative treatment is given which can help to reduce the effects of the disease on the pet's life, at least in the short term. Pain killers and other treatments can allow this in most cases.

Common cancers in pets

  • Lymphoma - cancer of the lymphatic system takes several forms. The commonest is where most of the lymph nodes in the body swell with malignant lymphocytes: this is multi-centric lymphoma. Otherwise, lymphatic tissue within other organs can develop malignant cells: the commonest sites are the intestine, kidneys, spleen and liver, though any organ can be affected. Lymphoma is treated by chemotherapy and 70-80% of patients will have a complete remission and be well. In cats, lymphomas are commonly caused by Leukaemia Virus. Vaccination of cats against this common virus is very effective protection.
  • Mammary tumours - about 50% of mammary lumps are benign when they first appear, but there is a significant risk of them becoming malignant. Early surgery is absolutely the best approach to mammary tumours. Spaying is excellent prevention from mammary tumours.
  • Skin tumours - the skin is reasonably visible on pets and, generally, skin tumours are noticed quite early by owners. Many skin bumps are benign tumours or just cysts, but there are some potentially nasty skin tumours, so it is always best to have any lump checked by a vet. The vast majority of skin tumours can be cured surgically if seen early.
  • Mouth tumours - owners do not often look in their pets' mouths, so many mouth tumours are comparatively large when first seen. The commonest symptoms are smelly breath, salivation, discomfort eating and bleeding from the mouth (also symptoms of dental disease). By the time any of these symptoms shows, the tumour is likely to be a fair size. Most vets will check pets' mouths when they see them for booster vaccinations, or during general examination and it would be hoped that tumours would be spotted then. If the tumour is at the back of the mouth, it can be difficult to see in the early stages except in a very cooperative pet. If mouth tumours are seen early enough, relatively minor surgery may be sufficient to cure them, but many will need major surgery. Many of these patients could benefit from radiotherapy, most mouth tumours are to some extent sensitive to radiotherapy. Chemotherapy is less used, though there are situations where it can be beneficial.
  • Gastrointestinal tumours - pets tend not to show symptoms until tumours in the intestine are quite large. Vomiting is often seen with gastric tumours at a fairly early stage, but these are not easy to diagnose except by endoscopy. Some intestinal tumours do not grow as lumps, but as a general thickening of the intestine: most patients with this type of disease will have diarrhoea. Surgery is the first line of treatment for tumours of the stomach and intestines. Radiotherapy or chemotherapy are less useful except in intestinal lymphomas.
  • Major organ tumours - the liver, kidneys, spleen, lungs, heart, reproductive organs and brain can all develop tumours. Removal can be difficult, and will depend on detailed assessment of the site and type of tumour. The spleen is quite commonly the site of tumours and if found in time, removal of the spleen can cure most. Surgery is the best option, but not all cases are suitable.

What can we do to reduce the risk of cancer in our pets? Prevention and early diagnosis are the key :

  • Spaying & castration
  • Vaccination of cats
  • Check every lump