Mammary Tumours

What are mammary tumours?

Mammary tumours arise mainly in female dogs from the elements of mammary tissue. The average age of affected dogs is 10 to 12 years, with such tumours being very uncommon in dogs under 5 years of age. The back teats are the most often affected.

Mammary tumours in male dogs are extremely rare. However, they are normally highly aggressive if they do occur.

What Causes Mammary Tumours?

Mammary tumour development is mainly hormone dependent. Research shows unspeyed dogs have seven times higher chances of developing mammary tumours  than speyed dogs. The chance of developing mammary tumours is virtually zero if desexing is done prior to the first season. A gradual increasing risk of tumour development is found when desexing is conducted between the first and fourth seasons. Desexing in bitches over 2 1/2 years of age appear to provide no protective effect.
 
Research also shows administration of progesterone compounds, such as Ovarid, have been associated with mammary tumour development.

Previous reproductive problems do not appear to be the causes for mammary tumours. The number or size of previous litters, previous episodes of pseudopregnancy, irregular or unpredictable seasons and previous fertility problems do not appear to influence the chance of mammary tumour development.

What Signs are Seen with Mammary Tumours?

Affected animals may present with one or several masses of varying sizes in the mammary tissues. These masses may appear as distinct nodules, which look like peas, or as a large swelling of the affected gland(s). Fluid secretion may be seen releasing from the nipples if the mammary ducts are affected and become cystic.

The tumours may spread to the lungs or other organs in some cases. Affected dog will be off food, vomit, have diarrhoea and/or have difficulty in breathing, depending on the parts of body affected.

How can Mammary Tumours be Diagnosed?
 
The appearance of lumps in the mammary tissue causes a suspicion of mammary tumour. Biopsies are taken for evaluation to confirm the tumours and find out their aggressiveness.

Overall biopsies have shown that about 50% of mammary tumours are malignant. The percentage of malignant tumours that recur or that cause the dogs' death within 2 years of surgery varies between 20% to 95%, depending on the degree of malignancy.

It is always advisable to X-ray the chest to assess if the tumours have spread to the lungs should mammary tumours be diagnosed. (If so, surgical removal of the mammary lumps will not provide a cure.)

What is the Treatment for Mammary Tumours?

Surgery is conducted to remove the affected tissue if the biopsies indicate that the tumour is not malignant.

Surgical removal with chemotherapy is required if the biopsies indicate there is a high probability for recurrence or spread. Results with chemotherapy are not always good. Radiotherapy has been tried but unsuccessful rate is high.

When the tumours are large, painful and cannot be successfully removed short term benefit may be achieved with the use of anti-inflammatories to relieve the soreness.