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Cancer in Dogs

Dogs are affected by cancer just as we humans are, and the disease can affect any of their organ systems, as well as their soft tissue and bones. Advances in medicine mean that nowadays, it is often possible for an early diagnosis to be made and for better treatment to be given, as there are specialised hospital departments for radiotherapy and chemotherapy.

What symptoms could be a sign of cancer in dogs?

The symptoms of cancer can take many forms, and often do not initially appear to indicate a serious illness at all. Many illnesses involving tumours develop gradually to begin with, which means that it is barely noticeable that anything is amiss with the patient.

Signs can include, among others:

  • Symptoms of feeling unwell: vomiting, loss of appetite, diarrhoea, constipation, sensitive stomach
  • Changes in behaviour: increased tiredness, fatigue, groaning, restlessness at night, disordered sleep, aggression/passiveness
  • Visible lumps (nodes) on various body parts, which may, among other things, affect mobility
  • Neurological abnormalities: cramps, symptoms of paralysis
  • Blood in the urine/stool

What to do if a tumour is diagnosed

One in five dogs will suffer from cancer at some point, and one in two over the age of ten dies from the disease. The risk of developing a tumour increases with age – the increase in pets’ average life expectancy has led to a rise in the number of cancer cases over the past decades. There are still some doubts surrounding why cancer begins to develop. Some possible causes could be genetics, immune disorders and carcinogenic chemicals and radiation. Passive smoking and sunburn, for example, are just as harmful for our four-legged friends as they are for us. Fortunately, the range of possible treatments has improved thanks to advances in veterinary medicine, and are now no longer limited to surgery.

Today’s cancer treatments

Depending on the type of tumour in question, the symptoms of cancer can vary considerably. Often, the beginning of the illness is characterised only by very general symptoms such as diarrhoea, vomiting, fever, weight loss, refusing food, and fatigue. A thorough diagnosis by the vet will shed light on what is going on. Once the type of tumour has been determined, an appropriate treatment plan will be worked out which includes surgery, chemo or radiotherapy, or a combination of these treatment methods. Accompanying pain therapy helps to assuage the dog’s suffering. The most common tumours in dogs affect the lacteal glands and lymph nodes, the skin, the muzzle area, the bones and the soft tissue.

A healthy lifestyle lowers the risk of cancer

Unfortunately, there is no guaranteed way to prevent cancer. A healthy lifestyle with plenty of exercise and high-quality food are, however, proven to lower the risk of cancer. Try to expose your dog to as little strong sunlight and as few exhaust fumes as possible, and choose a species-appropriate, natural feed free from synthetic flavourings and preservatives. If your dog already has cancer, do not delay getting treatment under any circumstances. Each day of waiting decreases your dog’s prospects of recovery, or of being able to extend their life. Ideally, take your dog to a cancer clinic for animals which uses the latest types of treatment.

Types of cancer in dogs

Tumours of the nose

While tumours of the nose are not particularly common, they are usually malignant. These tumours tend to affect older dogs over the age of eight years. Their malignant nature is due to the fact that these tumours are able to infiltrate (or grow into) the surrounding tissue. Metastases in nearby lymph nodes are also possible. Growth is usually slow and insidious, which unfortunately means that the illness is only recognised late on.

Symptoms:

  • Rhinitis = inflammation of the nasal mucous membrane with discharge (initially on one side) 
  • One-sided, later also two-sided stenosisation (narrowing) of the nasal cavity
  • Changes to the shape of anatomy in the nasal area or paranasal sinus area due to the tumour breaking through under the skin
  • Growth of the tumour into the oral cavity, the eye socket or via the ethmoid bone into the brain 
  • Often, obstruction (shift) of the tear duct or hindering of the outflow of frontal sinus secretions (making infections etc. more likely)
The vet will start by clarifying whether there may be another cause for these symptoms, such as benign destructive rhinitis due to aspergillosis (fungal infection) or chronic foreign body rhinitis. Other tumours, such as tumours which actually originated in the oral cavity or the eye socket and are now growing into the nasal cavity, may also be a possible cause of these symptoms. It is often not very easy for a diagnosis to be made, and the vet will need to use procedures involving images such as x-ray, CT scans or MRI scans. It is possible to investigate the tumour material further by taking samples using nasal wash, skin scrapes and fine needle aspiration. Treatment is also difficult. Curative treatment is not usually possible. The aim is to remove most of the tumour material by way of surgery, as far as this is possible, as well as to give accompanying chemo/radiotherapy under the supervision of a specialist. Unfortunately, the prognosis is always unfavourable for this type of tumour.

Skin tumours

Just as is the case in humans, there are a range of different tumours which can affect dogs’ skin tissue. These lumps can be both benign and malignant. Such tumours are often seen in middle-aged and older dogs. They range from the simple papilloma (wart) to squamous cell carcinomas and mast cell tumours. It is usually not possible to tell from outward appearance alone what type of tumour is present.


Symptoms:

  • Often no noticeable symptoms initially
  • Changes in the skin: lumps and bumps
  • In the case of larger lumps, there may also be restrictions to mobility, pressure sores or chafing of the lump, accompanied by inflammation
  • In case of malignant tumours that spread, additional organ symptoms are also possible over time

It’s important to examine your dog regularly for nodules and bumps, which you are bound to notice when you stroke your dog. In older dogs, lumps in the fatty tissue are common – so-called lipomas (fatty tumour). These are not skin tumours, however – they are instead considered tumours of the soft tissue. If they cause problems (by limiting mobility, for example), they can usually be removed easily and generally have a good prognosis. However, it is not possible to look at a lump from the outside and tell for sure whether it is really just a lipoma or in fact a different type of tumour. For this reason, lumps should always be checked with a doctor. The vet can take a tissue sample and have it tested in the lab in order to be sure. Lumps which have been surgically removed are also usually sent off for histological tests.
As is the case with any tumour, you should not wait too long to have a skin tumour checked out. If you discover a lump, it’s better to have it checked over early to find out what you’re dealing with. 
The treatment and prognosis for skin tumours depends on the individual type of tumour, as well as on its location and size.

One example:

 

Mast cell tumour

This tumour starts in the tissue mast cells of the skin, and is one of the most common skin tumour types. It behaves in a very unpredictable way biologically. 
It tends to be seen in older dogs especially, but occasionally also in younger dogs. Certain breeds are predisposed to this type of tumour, such as boxers, dachshunds, Bernese mountain dogs, labrador retrievers and schnauzers, as well as mongrels.

Symptoms:

  • Appearance can vary greatly
  • Tends to be found on the body and the limbs
  • Signs of malignancy: rapid growth, superficial disintegration of the nodules, appearance of satellite nodes, increase in size of primary lymph nodes
  • The appearance of the tumour can change rapidly due to the formation of oedemas (build-up of fluid in the tissue) and inflammation
  • Metastatic spread to the liver and spleen is possible later
  • Metastases in the lungs are relatively uncommon

What is particular about these tumours:

The granula (grain-shaped deposits) of the tumour cells contain messenger substances such as histamine. These can be released spontaneously or due to manipulation of the tumour, and can lead to so-called paraneoplastic symptoms: allergies, immune and inflammation reactions, low blood pressure, gastric ulcers, tarry stools and/or vomiting blood. 
For the diagnosis, the vet will take a sample (fine needle aspiration) and/or send the removed tumour material for a histological test.
The treatment includes the surgical removal of, if possible, the entire tumour, and may also include radiotherapy under the supervision of a specialist. Patients must undergo regular checks afterwards, as recurrences are common.
The prognosis depends on many factors: location of the tumour, stage of the cancer, age and breed of the dog. 
There is usually a bad prognosis for tumours which are poorly differentiated, which have developed metastases or which are located at a mucocutaneous junction (between the skin and a mucous membrane) or on a claw.

Lymph tumours

These are tumours of the blood-producing (hematopoietic) cells and lymphoid cells. They are malignant illnesses which come about as the result of the propagation of the blood-producing stem cells, and are associated with various cell maturation disorders.
A common tumour from this category is the malignant lymphoma (lymphosarcoma), a malignant tumour which originates in the lymphatic cells (such as the spleen, lymph nodes, bone marrow). 
Lymphosarcomas account for up to 80% of all hematopoietic tumours. They tend to be found in middle-aged and older dogs. Boxers, Basset Hounds, St Bernards and labrador retrievers have an increased risk of suffering from this type of tumour. 
After it has been established which part of the anatomy the cancer is located in, it can be defined as being multicentric (emanating from several centres), mediastinal (emanating from the mediastinum), alimentary (emanating from the gastrointestinal tract), extranodal (outside of a lymph node) or as being a skin type. 
The most common form, at 85% of cases, is multicentric:

Signs can include:
  • Painless enlargement of the lymph nodes, particularly in the shoulder (neck) and the hollow of the knee, enlargement of the spleen and liver as well as infiltration of the lungs and/or bone marrow
  • May be asymptomatic initially
  • Then general symptoms later: listlessness, lack of appetite, fever, emaciation


Alimentary:

  • Diarrhoea, loss of appetite, vomiting, bowel obstruction, emaciation

Mediastinal:
  • Coughing, shortness of breath, formation of oedemas, pleural effusion


Extranodal lymphosarcoma:

  • rare, can be a lymphatic infiltration of the central nervous system, of the spinal cord, the skin, the nose, the larynx etc.


Skin type:

  • Distinction between epitheliotropic (focal or generalised reddened to flaky dermatitis with ulcers or papule formation = widespread changes to the skin) and non-epitheliotropic (affecting the middle and lower layers of the skin)

Overall, the clinical presentation of the malignant lymphoma is mainly shaped by which organ it is located in.


Diagnosis:

Blood tests, image procedures (x-ray, ultrasound), aspiration cytology of altered lymph nodes, of the spleen, liver and bone marrow, and biopsies


Treatment:

Treatment by an oncologist (surgery, palliative radiation, chemotherapy). The aim is for treatment to begin as early as possible in order to enable the dog to enjoy good quality of life in remission, and for the remission to be maintained by way of maintenance treatment.


Prognosis:

Very bad without treatment. With treatment, the prognosis depends on the location and stage of the cancer. With treatment and favourable circumstances, a life expectancy of one year or more can be achieved.

Gastric tumours

Gastric tumours make up around 2.5% of all tumours in dogs. The majority of them present as adenocarcinomas, followed by lymphomas, malignant mesenchymal tumours, leiomyomas, leiomyosarcomas, undifferentiated sarcomas and fibrosarcomas. Adenocarcinomas have a certain tendency towards early metastatic spread in the mediastinal lymph nodes, the liver, and to some extent in the lungs.
They tend to be found in middle-aged and older dogs. 
Gastric tumours tend to be located in the vicinity of the pylorus (exit point from the stomach) and of the lesser curvature of the stomach. 
Malignant tumours appear imposing as masses protruding into the lumen, as crater-shaped ulcers or as a hard, poorly defined thickening of the stomach wall.

Symptoms:

  • Benign tumours often remain symptomless
  • Malignant tumours: vomiting, loss of appetite, emaciation, listlessness and usually blood in the stool (not visible to the naked eye) and pain when the stomach area is touched
  • In older dogs, vomiting blood is always a reason to consider the possibility that the dog may be suffering from a gastric tumour.

For the diagnosis, an image procedure is carried out (x-ray, ultrasound) and a tissue sample is taken. Treatment is difficult and it is recommended that a specialist be consulted. If it is possible for an operation to be carried out, surgery may be conducted, as well as chemo/radiotherapy.

Prognosis:

Benign tumours such as leiomyomas or adenomatous polyps can usually be removed effectively by way of surgery (curatively). The prognosis for malignant tumours is bad.

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