Mammary Tumours in Dogs (Breast Cancer)

A beagle after mammary tumour removal

Mammary tumours are the most common type of cancer in female dogs and are usually surgically removed.

If you can feel a lump in your dog’s teat, alarm bells should ring. We have summarised for you how it could be breast cancer and how your vet can detect and treat mammary tumours in dogs.

Symptoms: What are the signs of a mammary tumour in dogs?

The primary symptom of breast cancer in dogs is when one or more lumps can be found in the teat and mammary gland area. They usually feel rough and affect one or both teats. 

If the tumour becomes inflamed, the tissue can swell further and prove very painful for your dog. In this case, many dog owners confuse the warm, reddened area with a mammary gland inflammation (mastitis). 

Diagnosis: How is a mammary tumour detected in dogs?

Most owners notice a mammary tumour in dogs if they find small lumps on their dog’s teats. If you can sense circumferential growth, you should definitely get it looked at by a vet. 

The vet touches the growths, the surrounding gland tissue and your dog’s regional lymph nodes. With the help of an X-ray examination, it’s possible for them to observe the tissue more closely and find potential secondary tumours (metastases) in other organs. 

An ultrasound (sonography) also helps the vet to detect changes in the abdomen and assess the malignancy of the tumour based on the echo pattern. 

Blood and tissue samples help with the diagnosis

In addition, the vet takes blood from your dog. Using specific parameters, they can more accurately assess kidney and liver function. If the cancer is advanced, it’s also possible to detect tumour markers in the blood. 

Sometimes the vet will also take a tissue sample and send it to a laboratory for examination. However, this alone is not always enough to make a certain diagnosis. 

A mammary tumour in a female dog's teat
How breast cancer in dogs can look: a bulky increase in circumference on the teats.

Treatment: How is breast cancer treated in dogs?

Normally vets treat a mammary tumour in dogs surgically and not with chemotherapy. If the cancer is still in an early stage, it can also be beneficial to wait until the tumour reaches a certain size. This allows the vet to create the best conditions for a successful operation. 

If only one teat is diseased, it can be sufficient just to remove that one. If both are affected, your vet will have to cut extensively around the tissue and possibly remove all the mammary glands. 

In any case, it’s important that you regularly take your dog to the vet after surgery. The vet can detect a relapse of the mammary tumour at an early stage and take countermeasures. 

Prognosis: How dangerous is a mammary tumour in dogs?

Mammary tumours in dogs unfortunately have quite a high relapse rate in general. This means that despite being successfully removed, the tumour will form again after some time. 

The malignancy of breast cancer also depends on the following factors: 

  • Type of cancer 
  • Size of the tumour 
  • Degree of infiltration (spread amongst the teats) 
  • Histological degree of malignancy 
  • Age of the dog 
  • Involvement of the lymph nodes 

If the tumour has spread (metastasised) to other organs, such as the lungs, this also has a negative impact on the prognosis. 

Other factors can likewise impair life expectancy. For instance, the prognosis also depends on the dog’s diet. It’s important that your dog doesn’t lose any weight and builds muscle. A diet rich in fat and calories plays a big role here, because it helps your dog to counteract severe weight loss. 

Causes: What triggers a mammary tumour in dogs?

Dog teats are a compound gland. It changes cyclically depending in the hormone cycle – especially the hormone progesterone. 

Since the glands consist of different cell types, there are also different tumour types of breast cancer. It’s not uncommon for mixed forms to arise from different cells. Hence, specialists divide mammary tumours in dogs as follows depending on the cells involved: 

Malignant tumours  Benign tumours  Pathological hyperplasia (enlargement) or dysplasia (malformation) of the mammary gland 
Non-invasive carcinoma  Adenoma  Ductal hyperplasia 
Complex carcinoma  Fibroadenoma  Lobular hyperplasia (pathological enlargement of the gland lobules) 
Simple carcinoma  Benign mixed tumour  Cysts 
Special types: Spindle cell, squamous epithelium, mucinous and lipid-rich carcinoma  Intraductal papilloma  Duct ectasia 
Sarcoma (e.g. fibro- or osteosarcoma)    Focal fibrosis (pathological proliferation of the connective tissue) 
Carcinosarcoma    Gynaecomastia (enlargement of the mammary glands in males) 

Occurrence: Which dogs are affected more frequently? 

The mammary tumour is the most common tumour in female dogs. Nevertheless, it’s possible for males too to suffer from this form of cancer. 

Whilst hybrids generally suffer from it less often, pedigree dogs of certain breeds can be more or less prone to breast cancer. For example, Collies have a lower risk, whereas DachshundsPoodles or Pointers suffer from this disease more often according to studies. 

Along with the sex and breed, the dog’s age also determines the risk of contracting the disease. Mammary tumours occur more often in older dogs, roughly between nine and eleven years of age.

A vet will perform an ultrasound scan on the dog
With the help of sonography, the vet attempts to assess the malignancy of a tumour.

Prevention: Can mammary tumours in dogs be prevented?

There are some possibilities to reduce the risk of breast cancer for your dog. Whilst pregnancy plays no role in this, you can protect your dog from breast cancer with the following measures: 

1. Spaying 

If you get your dog spayed early on, the probability of it suffering from breast cancer is lower. However, opinions vary as to the best time for spaying, although vets generally recommend it between the first and second heat period. 

2. Diet 

Obesity is known to trigger mammary tumours in dogs. Hence, you should make sure to give your pet a healthy, balanced diet. Adapt quantities of food to your dog’s needs. Also ensure that your dog can always get sufficient exercise. 

3. Avoid hormone treatments 

Hormones, more specifically gestagens like progesterone, promote the occurrence of mammary tumours in dogs. If you’re considering a hormone treatment, you should only make this decision in consultation with your vet. 

4. Genetic tests 

A mammary tumour in dogs can be of genetic origin. Although there are special tests to detect mutations in tumour suppressor genes, the result isn’t always conclusive. 

5. Precautionary examination 

If your dog is slightly older and has not been spayed, it’s particularly recommended to get it checked by a vet every year. This way, you can identify and tackle the onset of a mammary tumour at an early stage. 

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