The basics
What is cancer?

The body is made of many building stones, cells included. Cells multiply a limited number of times after which they die. The old cells are then replaced by new ones.

The more a cell multiplies, the higher the risk becomes that these multiplications are accompanied by mutations/mistakes. These mistakes or mutations can be the result of a coincidence, but also of exposure to environmental factor such as UV radiation or smoke particles.

Normally, these mistakes are recognized by the control mechanisms of the cell. The mistake can then be fixed or the cell dies. Sometimes the cell can escape these control mechanisms and start to multiply without limits. At that moment, the cell has become a cancerous cell.

When cancer cells multiply in a uncontrolled way, a tumour forms. The more cells multiply, the larger the tumour gets. The faster the cells multiply, the more malignant/high-grade the tumour becomes.

When the tumour reaches a size of 1-2 millimeter, the cancer cells need blood vessels to continue growing. They are capable of influencing the surrounding tissue in such a way that it will allow new blood vessels to be formed in the direction of the newly formed clump of cancerous cells.

A few terms

Tumours (also called cancer or neoplasia) consist of cancer cells and can be benign or malignant.

Benign tumour

Benign tumours are masses that contain cancer cells that in general do not invade the surrounding tissue and does not spread throughout the body (metastasize) towards other parts of the body. In general, they form a mass in the body that takes in place, and causes only problems when it presses on other organs or tissues because of a lack of space. For example, the pressure on nerves can cause pain or a malfunction of the innerved member. The benign masses can sometimes evolve to a malignant one.

Malignant tumour

Malignant tumours are masses that contain cancer cells that are typically capable of invading the surrounding tissue and spread. For this purpose, the cancer cells diffuse substances (such as growth factors) that incite the healthy tissue surrounding the tumour to cooperate with the tumour in order to facilitate its growth.


When cancer cells invade healthy surrounding tissue and escape the tumour (the primary tumour) via the blood or lymph to arrive in other organs and there form a new tumour (secondary tumour). This secondary tumour is a metastasis. The cancer cells of a metastasis are made from the same type of cell as the primary tumour. For example, a bone tumour can metastasize towards the lungs and produce bone tissue in the lungs.

Remission / regression

When a disease gives way and the patient temporarily feels better, the patient is in remission. When all the signs of the disease have disappeared, this is a complete remission. However, this does not mean that the disease is completely eliminated. During remission, there are 2 possibilities: the cancer cells are gone, or the masses are too little to detect. A tumour is in regression when it becomes smaller.

The longer a remission takes place, the higher the chances are that the patient is completely cured.


A relapse takes place when the tumour comes back after having been away for a period of time (this is the end of a remission).


What is staging?

Staging involves determining 3 types of information via the TNM system:

  1. The size and location of the tumour (T)
  2. Lymph node involvement (N)
  3. The presence of metastases (M) in tissues other than lymph nodes near the tumour

This information is needed to conceive the best possible treatment plan for your dog. The tumoural progression stage determines the treatment plan and prognosis. The treatment plan also takes into account the general health of the dog (e.g. check of issues with the heart / kidneys / liver) to administer the most appropriate treatment.

As in humans, even with the most modern research techniques, it is not always possible to detect very small metastases.

Depending on the tumour type, the staging can be more or less elaborate (see tumour types). It depends on the predicted behaviour of the tumour. Some examples:

  • To diagnose a mast cell tumour, a tumour of mast cells (variety of white blood cells), it is necessary to do a punction / biopsy of the tumour, a punction of the regional lymph nodes, ultrasound (and if possible punction) of the liver and spleen.
  • For osteosarcoma, a bone tumour, it is necessary to perform a puncture of regional lymph nodes, an X-ray of the lungs and bones (also possible via scintigraphy) and a blood analysis. A CT scan is more sensitive to find metasases in the lungs and is more available than scintigraphy.