Cat & Dog - Eye Tumours - Intra-orbital except Melanomas

These notes are provided to help you understand the diagnosis or possible diagnosis of cancer in your pet. For general information on cancer in pets ask for our handout What is cancer. If not already performed your veterinary surgeon may suggest certain tests to help confirm or eliminate the diagnosis, and to help assess treatment options and likely outcomes. Because individual situations and responses vary, and because cancers often behave unpredictably, science can only give us a guide. However information and understanding of tumours in animals is improving all the time.

We understand that this can be a very worrying time and we apologise for the need to use some technical language. If you do not understand anything please do not hesitate to ask.

What are these tumours?

These are tumours arising from structures within the eye. They tend to result in an increase in the internal pressure (glaucoma), which then leads to blindness. There is sometimes bleeding within the eye, swelling and pain.

The most common eye tumours originate from the melanin-producing cells (these are discussed in a separate handout). The second most common group affects the iris and ciliary body (anterior uveal tract) causing non-cancerous iridociliary cysts, benign adenomas and malignant adenocarcinomas. These are rare tumours of the nervous tissue in the eye and, in cats, a malignant tumour that occurs as long as ten years following an injury to the lens ('feline primary ocular sarcoma' or 'post-traumatic sarcoma'). Blue-eyed dogs also have a specific benign tumour of the iris (spindle cell tumour). Some tumours originate elsewhere in the body but settle and grow in the eye as metastases. The most common of these are tumours of lymphoid cells (lymphosarcoma or lymphoma).

What do we know about the cause?

The reason why a particular pet may develop this, or any cancer, is not straightforward. Cancer is often seemingly the culmination of a series of circumstances which come together for the unfortunate individual.

Feline primary ocular sarcoma follows injury to the eye of cats and the spindle cell tumour of blue-eyed dogs has genetic factors implicated. Little is known about causes of the other tumours.

Why has my animal developed this cancer?

Some animals have a greater tendency (genetic susceptibility) to cancer. Some breeds have far more cancers than others, often of specific types. The more divisions a cell undergoes, the more probable is a mutation so cancer is commoner in older animals but a few rare tumours are developmental problems so they occur in young animals.

Are these common tumours?

These are all rare tumours. Iridociliary cysts and tumours are the most common of this group in dogs, but in cats they are very rare. Lymphosarcomas originating from lymphoid cells are most common in cats.

How will these cancers affect my pet?

Even benign tumours cause glaucoma (increased pressure inside the eye), which causes loss of sight; so iridociliary cancers are clinically important even when small in size. They are often suspected even when direct observation of the tumour is impossible because they cause glaucoma or intra-ocular haemorrhage. Other tumours form nodules and swellings or opacities, which can be seen by examination with an ophthalmoscope. Small tumours may show no clinical disease at the time of diagnosis but others cause uveitis (inflammation), glaucoma (increased ocular pressure), haemorrhage (bleeding) or optic nerve compression. All these will result in blindness. The feline post-traumatic sarcoma is highly malignant and spreads all round the eye and into adjacent tissues causing opacity (non transparency) of the eye, swelling, pain and blindness.

How are these cancers diagnosed?

Clinically, cancer may be suspected by swelling or opacity or redness inside the eye. Ultrasonography may help to delineate (look at) the masses when they are not visible. Accurate diagnosis of the tumour and prediction of behaviour (prognosis) rely on microscopic examination of tissue (histopathology). This is done at a specialised laboratory by a veterinary pathologist.

What types of treatment are available?

Unfortunately, surgical removal of these tumours involves removal of the eye.

Can these cancers disappear without treatment?

Cancer very rarely disappears without treatment. Very occasionally, spontaneous loss of blood supply to the cancer can make it die but the dead tissue will still need surgical removal. The body's immune system is not effective in causing these tumours to regress (shrink).

How can I nurse my pet?

After surgery, an 'Elizabethan collar' may be provided to prevent your pet rubbing his or her eye and interfering with the operation site, which needs to be kept clean. Any loss of stitches or significant swelling or bleeding should be reported to your veterinary surgeon.

Specific treatment may include eye drops and ointments with antibiotics and anti-inflammatory drugs.

If you require additional advice on post-surgical care, please ask.

How will I know how the cancer will behave?

Histopathology will give your veterinary surgeon the diagnosis that helps to indicate how it is likely to behave. The veterinary pathologist usually adds a prognosis that describes the probability of local recurrence or metastasis (distant spread).

How will I know if the cancer is permanently cured?

'Cure' has to be a guarded term in dealing with any cancer.

Almost all of these tumours (including iridociliary cysts and tumours and rare tumours such as medulloepithelioma and iridal spindle cell tumour of blue eyed dogs) can be cured by removal of the eye.

Post-traumatic sarcoma of cats is highly malignant and the tumours recur and spread into the optic nerve and other adjacent tissues with possible distant metastasis. Surgical cure cannot be guaranteed.

Tumours that have spread (metastasised) from elsewhere in the body usually indicate widespread, advanced disease and, sadly, cure is not possible. Amongst these are lymphosarcoma and haemangiosarcoma.

Are there any risks to my family or other pets?

No, these are not infectious tumours and are not transmitted from pet to pet or from pets to people.