What is cancer?

• Benign tumours are not cancer. They usually grow slowly and push away healthy tissue. They do not
  spread to other parts of the body. If a benign tumour is large, it can press on other body organs or structures and cause bleeding or pain.
• Malignant tumours are cancer. A malignant tumour is able to invade and destroy surrounding tissue.
• Metastatic tumours grow from cancer cells that have travelled to another part of the body (Fig. 2).
  The original tumour, called the primary tumour, is the source of the cancer cells. The new tumour is called the secondary tumour. Cancer cells can spread through the blood (haematogenous metastasis) or through the lymph vessels to the lymph nodes (lymph node metastasis).

Prostate cancer can sometimes spread to the bones and cause another tumour to grow there. When this happens, the cancer cells from the prostate (primary cancer) have travelled with the blood to the bones. The new tumour (secondary cancer) is called a bone metastasis of prostate cancer.

Different cancers spread to common sites or organs, usually in a typical pattern. Cancer can spread to any part of the body, but this is more rare. The process of metastasis is complex, and many factors come into play. Of a few thousand cancer cells, it is thought that only few survive and are able to grow in another part of the body.

If the doctor thinks micrometastases are likely, drug therapy can be given to try to kill the remaining cancer cells before they can grow into macrometastases.

• Micrometastases contain very few cells and can only be seen in a tissue sample under a microscope.
• Macrometastases are large enough to be seen with an imaging test such as a CT scan or MRI.

Cancer starts in the body’s cells. An unrepairable change or error of the genetic code of a cell may lead to mutation and cancer.

Not every mutation leads to cancer. Mutations can be inherited, which means they are in the genes already at birth, or they can occur during your lifetime. Mutations can occur by chance, without a known cause. Sometimes they are the result of stress caused by harmful substances in the environment, such as sunlight, air pollution, cigarette smoke, alcohol, or chemicals. Exposure to harmful substances can increase the risk of getting cancer.

Why does cancer sometimes come back?

Doctors do their best to destroy all cancer cells, but sometimes cancer comes back even after a long time. Cancer cells may have spread or gone into a state of rest somewhere in the body and eventually grow there. Sometimes not all cancer cells are removed during surgery or killed by chemotherapy or radiation; these cells can grow and produce a new tumour of the original cancer at the same place (relapse). In addition, cancer cells are very effective at adapting to new conditions and can become resistant to certain types of treatment.

After cancer treatment, you are scheduled for follow-up visits with your doctor. It is important to attend these visits. Your doctor can suggest additional treatment if there are signs of tumour cells remaining in the body.

Cancer can arise from cells in different tissues and organs in the body (Table 1). For example, a primary cancer that develops in the breast is called breast cancer. Cancer will have different names depending on the tissue of origin.

Your doctor might notice signs or symptoms of cancer during a medical examination. If cancer is suspected, some tests are performed. A physical examination is carried out and some form of imaging will take place. Small quantities (samples) of blood and/or tissue from your body are often taken to be studied by a pathologist. The pathologist uses a microscope and special techniques like cell staining and molecular tests to make the diagnosis.

Treatment is based on your type of cancer as well as your overall health and preferences. It may involve surgery, chemo-/immunotherapy, or radiation, or combinations. Clinical trials may be available to study new treatments such as immunotherapy or gene therapy. Your doctor works with a multidisciplinary team to guide your treatment.

Cure or remission?

A lot of cancers can be cured today, but your doctor might hesitate to tell you that. Some cancer cells might have remained somewhere and are too few to cause symptoms, cannot be detected, or are dormant. This state is called remission, which means that no cancer is detectable at this time. When your cancer is in remission, only time can tell whether it is cured or not. You may still get check-ups, scans, or even get treatment to remove remaining cancer cells.

Interpreting cancer statistics – How to read the numbers

Statistics cannot tell what exactly will happen to you, but they provide good general indications. Because every cancer is unique, no statistic can give exact answers about the outcome of your cancer.

All statistical measures regarding Europe were taken from the EUCAN fact sheets http://eco.iarc.fr/eucan/CancerOne.aspx?Cancer=29&Gender=1