Cat & Dog - Uterus, Vagina and Vulva Tumours

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?

Most swellings and tumours of the uterus are not cancerous (except in rabbits). The commonest in the bitch is cystic endometrial hyperplasia (overgrowth of the inner lining of the uterus) due to hormone stimulation. Sometimes, this reaction is deeper in the muscle layers and is called 'adenomyosis'. Secondary infection and inflammation then convert the endometrial hyperplasia into a serious condition called pyometra (literally pus in the womb). Cysts and polyps of the endometrium can also be part of the pyometra syndrome or be due to congenital abnormalities. They may persist when the cause is removed and may be multiple.

Endometrial cancers may also be multiple. Benign adenomas of the endometrium are rare. Malignant tumours (adenocarcinomas) may spread (metastasise) to lymph nodes and lungs, often when the primary tumour is still small in size.

Tumours also form in the smooth muscle layers (leiomyomas). These are most common in the vagina of the bitch. They are benign and problems are physical effects, related to the site and size of the tumour. Leiomyomas are, at least in part, hormone dependent so removal of the ovaries is an integral part of the surgical management as it is effective in both preventing development and recurrence.

A few tumours are cysts formed in glands of various areas. They are uncommon in the vagina and can regress (shrink) spontaneously. In the vagina, there may be small, viral, benign fibropapillomas (similar to human warts)that regress spontaneously in a few months. Malignant tumours in this area are rare but around the vulva, locally recurrent squamous cell carcinomas, similar to those of the skin can be seen. Urothelial carcinoma can also spread downwards from the bladder into the urethra.

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.

Endometrial hyperplasia (overgrowth) of the uterus (womb) is usually due to stimulation by the natural female hormone progesterone during the long (luteal) phase between seasons in the bitch and queen. It can also be induced by the female hormone oestrogen. This may be the animal's own hormone (produced by tumours of the ovary or ovarian cysts). External sources of oestrogen and progesterone given for medical reasons can also induce the same pathology. Infection usually enters through the vagina and is able to establish itself when progesterone is the major hormone. Cysts are usually secondary to overproduction of secretions due to hormonal stimulation, blockage of the ducts or infection.

Although sex hormones are the most important single factor increasing the risk of developing cancer of the uterus, uterine adenocarcinomas do not seem to require prolonged hyperoestrogenism conditioning (unlike the situation for women). Removal of the ovaries and uterus (ovariohystectomy or spaying) prevents all these conditions.

Smooth muscle tumours (leiomyomas) are hormone dependent. Fibropapillomas and papillomas are due to papilloma viruses that do not affect other species of animals or humans. Urothelial carcinomas are similar in cause to bladder tumours and may be caused by trauma, infection or chemicals. Female dogs have a predilection for these tumours and most have female hormone receptors suggesting hormones may be needed at some stages of development. Squamous cell carcinoma of the vulva usually has UV (sunlight) initiation.

Why has my animal developed this tumour?

Some animals have a greater tendency (genetic susceptibility) to certain diseases, particularly cancer. The more divisions a cell undergoes, the more probable is a mutation so cancer is commoner in older animals. Hormone irregularities will make an animal more likely to have smooth muscle tumours. Once tumours are malignant, they are no longer influenced by hormones.

Are these common problems?

Cystic endometrial hyperplasia with or without secondary inflammation is common in unspayed dogs and cats. Uterine cancers are rare in both cats and dogs. Tumours of the cervix are very rare in dogs and cats.

Smooth muscle tumours and polyps of the tubular part of the genital system are common in the bitch and queen. They are commonest in the vaginal wall and may be single or multiple and up to 10 cm in diameter. As they grow, they develop abundant collagenous stroma (white firbrous tissue) and become firm in texture so are known as 'fibroleiomyomas' or fibroids. Biological behaviour is the same for all of them.

All the other tumours of this area are unusual or rare.

How will this affect my pet?

Many bitches show other effects of hormone imbalance before development of tumours. These include abnormal seasons or persistent oestrus. Later, uterine problems often result in discharge from the vagina. Sometimes, a swollen abdomen is the main sign. Some animals have difficulty or pain passing water (urinating) or develop a secondary infection or they pass fresh blood in the urine. When the uterus is infected, bitches may have loss of appetite, vomiting, lethargy, weakness, pyrexia (fever) and anaemia.

The most obvious effect of leiomyomas of the vagina is swelling in or around the area, sometimes with large parts of the inside turning outwards and becoming visible. There may be discharge due to secondary infection, haemorrhage and ulceration.

Urothelial carcinomas usually cause difficulty or pain on urination. Papilloma clinical signs will vary with the site, number of tumours and their size. Ulcers and external growths are usual in squamous cell carcinoma.

A few malignant tumours may not be noticed until there is weight loss, illness and lethargy associated with anaemia, secondary infection of the uterus or secondary tumours. If the cancer metastasises to the lungs, there may be shortness of breath and difficulty breathing.

How are these conditions diagnosed?

Clinically, uterine conditions can be difficult to diagnose unless there is vaginal discharge. Blood tests sometimes help as there may be changes in the blood cells secondary to hormone abnormalities and infection. Increased blood hormone levels are not reliable for diagnosis.

Once the uterus is removed, definitive diagnosis of the problem and prediction of behaviour (prognosis) relies upon microscopic examination of tissue (histopathology). This is done at a specialised laboratory by a veterinary pathologist.

Clinically, vaginal conditions are usually suspected from the clinical signs and history. Histopathology will give a diagnosis and prognosis.

'Basic fibroblast growth factor' in the blood is used to detect urethelial tumours in people.  It has been found in the urine of dogs with bladder cancer, it is not specific for the tumours and false positives are seen in other diseases.

What types of treatment are available?

The usual treatment for uterine diseases is surgical removal of both ovaries and the uterus. Other treatments are not generally available and their effectiveness is unknown.

The usual treatment for vaginal leiomyomas is surgical removal of the tumour and both ovaries and the uterus. Cysts in the vagina are also removed or the lining that produces the fluid destroyed. Papillomas and squamous cell carcinomas are often removed surgically. Urethelial carcinomas may be surgically reduced in size but full removal is usually impossible because of the site. Non-steroidal anti-inflammatory drugs may be used to help in the treatment of these tumours.

Can these conditions disappear without treatment?

Endometrial hyperplasia tends to be progressive and remains in the uterus unless there is removal of the hormonal stimulus (from the ovaries or hormone therapy). The infection can, sometimes, be treated medically if the womb is open.

Unless the hormone stimuli are removed, leiomyomas will not regress. Infections can be treated medically and papillomas usually regress spontaneously in a few months through the activity of the body's immune system. The openings of cysts may unblock so they disappear.

The body's immune system is not effective in causing these malignant cancers to regress. Multiple tumours are also common.

How can I nurse my pet?

After surgery, the operation site similarly needs to be kept clean and your pet should not be allowed to interfere with the site. Any loss of sutures or significant swelling or bleeding should be reported to your veterinary surgeon. You may be asked to check that your pet can pass urine and faeces. If you require additional advice on post-surgical care, please ask.

Pyometra can make your pet ill so post-operative special diets and nursing may be required until she has restored kidney and liver function and the circulation and blood have returned to normal. Please ask if you need more advice.

When will I know if there is a permanent cure?

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

Histopathology will give your veterinary surgeon the diagnosis that will indicate the nature of the tumour and how it is likely to behave.

Within a few weeks, you should know whether uterine cancer has been removed in time to prevent spread to other parts of the body.

All the benign tumours of the vagina should be cured by surgery or spontaneous regression. Only the malignant tumours (urethelial carcinoma and squamous cell carcinoma) cannot always be permanently cured. Urethelial carcinoma is often not curable because of the site and the stage of disease but squamous cell carcinomas can usually be cured surgically without spread to other parts of the body.

Are there any risks to my family or other pets?

No, these are not contagious diseases and are not transmitted from pet to pet or from pets to people.