Cancer metastases: what are they?

What is a metastasis? 

Cancer is a disease caused by cell mutation: these cells become abnormal and proliferate excessively. They form a mass called a malignant tumor.  

A cancer cell can grow, divide and spread into the tissues or structures around it. It can also spread to other organs.  

When cancer cells from an initial tumor (or primary tumor) migrate through lymphatic vessels or blood vessels to another part of the body and take up residence, forming a new tumor, this is called metastasis, or secondary tumor.  

Metastases most often develop in the lungs, liver, bones and brain. However, no matter where it is located, a malignant tumor is always defined by its tissue of origin. Lung cancer that spreads to the bones does not become bone cancer, it is still lung cancer. Metastases are, in fact, secondary locations of the same tumor.

The risk of developing metastases depends on the characteristics of the primary tumor. There are several things to consider: the type of cancer, the size of the tumor and its location, how fast it grows, how likely it is to spread and how long it has been in the body.  

Almost all cancers can become metastatic except for some skin cancers. Each type of cancer has its “preferred” location for metastases development. For example: lung cancer most often metastasises to the lymph nodes while breast cancer - to the bones or lungs.

What symptoms do metastases cause? How are they diagnosed?  

The symptoms of metastases vary depending on the organ affected. They can develop very quickly after the initial diagnosis or several years. Some cancers never metastasise, some cancers metastasise a lot.

There are several types of metastases and the symptoms that appear are linked to the organ “colonised” by cancer cells:  

• Bone metastases: symptoms of bone pain, fractures, vertebral compression and/or hypercalcaemia,
• Cerebral metastases: a wide variety of symptoms depending on the area of the brain affected, nausea, vomiting, dizziness, poor concentration, muscle weakness and/or hemiplegia,
• Lung metastases: symptoms of pain, persistent cough, shortness of breath, breathing difficulties and/or coughing up blood,
• Liver metastases: symptoms of heaviness and pain in the liver, fever and/or jaundice.
  
  

Other signs that may indicate the progression of a primary cancer to metastatic cancer include fatigue, pain, loss of appetite, headaches, mood swings and abnormal bleeding.  

A cancer can become metastatic and be diagnosed at 3 different stages:  

• When the primary tumor is discovered, during the complete evaluation of a patient which is carried out to identify the organs affected; these are called synchronous metastases,  
• Several months or years later, when cancerous cells affect another organ even though the initial tumor has been treated, these are called metachronous metastases,  
• When investigating the cause of symptoms caused by metastases.
  
  

To diagnose metastases, several examinations can be carried out: a clinical examination, biological examinations (blood and urine), medical imaging (ultrasound, CT scan, X-ray, scintigraphy, PET scan) and also, a search for tumor markers.  

Medical imaging techniques allow the exploration of organs affected by cancer or metastases but it is the biopsy that actually confirms the presence of the tumor cells.  

In reality, it is difficult to diagnose metastases at an early stage, as in the case of a patient in remission, for example, there is no systematic examination, so if cancer cells are dormant, they may be detected too late.  

How can metastases be treated?  

The treatment of metastatic cancer depends on the location and characteristics of the new tumor(s). In general, during the treatment of the primary tumor, adjuvant treatment is given as a safety measure to prevent metastases and the risk of recurrence (reoccurrence of the cancer in the same place).

Metastases retain the characteristics of the primary tumor, so their treatment will be based on the same therapeutic strategies as those used for the initial tumor. Where possible, some metastases can be removed by resection surgery (an operation to remove all or part of an organ or tissue).

To block the proliferation of tumor cells, chemotherapy, hormone therapy and targeted therapies may be used. It is also possible to act on the patient's immune system with immunotherapy.

In the case of brain metastases, the only options are radiotherapy and surgery to remove the tumor.  

In the case of bone metastases, a cementoplasty can be performed, which is an injection of cement into the bone or vertebrae, to consolidate them and reduce pain.

Is it possible to live with metastases?  

In general, metastatic cancers progress more rapidly than the primary cancer, they are complex cancers and their cells are resistant to treatment.  

If an organ is affected and the tumor has spread significantly, the prognosis may be life-threatening. This is known as generalised cancer, or stage 4 cancer.

However, thanks to new technologies, there has been an improvement in the lifespan of patients in certain types of cancer such as lung cancer, melanoma and HER2 breast cancer.  

Today, it is rare to cure metastases. The disease is not curable but it is treatable and patients can live a long time with metastases. Various treatments and surgeries can regress metastases and limit their complications.

Many patients live with ongoing therapies. Pain management and supportive care are key elements for improving patients’ quality of life.  

The mechanisms of the metastatic process are still poorly understood, the proliferation of cancer cells from the primary tumor can occur very early, while some of these cells can remain dormant without us knowing why.  

Most research today is focused on the early detection of cells associated with poor prognosis. One of the recent breakthroughs gives hope: scientists are now able to detect circulating cancer cells, leading to the rapid initiation of targeted treatment which prevents the cells from growing elsewhere. 

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