Professor David Reynders

Differences between Cancer Cells and Normal Cells

The human body is made up of trillions of cells. Every human though, starts as a single cell, this cell then divides and replicates creating new cells each new cell is programmed to become part of the human body having its own unique and special function.


The cells are controlled and managed by DNA. On the DNA there is a series of switches both on-and-off which determine which function the cell perform. If the cell is no longer needed or is not functioning properly the cell goes through a process called apoptosis. This is a process whereby the cell naturally dies when it is no longer needed or not functioning correctly.

How Cancer Arises

Cancer arises when the cells ignore the normal signals to stop dividing when they are no longer needed or undergo the process of apoptosis, (the natural death when it is no longer needed).

These bad or dysfunctional cells have lost the ability to naturally die but have gained ability to self-replicate and as result produce massive balls of dysfunctional cells, we call this a tumour or a cancer.

The cancer or tumour cells are able to influence normal cells and molecules and blood vessels that surround and feed the tumour.  Cancer cells can induce normal nearby blood vessels to supply these tumours with oxygen and nutrients which they need to grow. The blood vessels also remove the waste products from the tumour.

In essence the tumour cell is a previously normal cell that has gained the ability to reproduce itself and lost the ability to decide when to stop and when to die. They do not function as normal cells but rather take over the space where normal cells should be. This stops or limits the normal functioning of the body and if left untreated often will result in death.

When and how Cancer Spreads

Tumour cells can break away from the first formed primary cancer, they travel through the blood and the lymph system to form new tumours, (metastatic tumours) in other parts of the body. Metastatic tumours are the same type of cancer as the primary tumour. The process whereby a tumour spreads is called Metastasis.

For example Wilms tumour or kidney cancer often spreads to the lungs via the bloodstream. The new cancer in the lungs if viewed under a microscope is exactly the same as the tumour cell found in the kidney.

Types of Cancer

The types of cancers that occur most often in children are:

  • Leukemia
  • Brain and spinal cord tumours
  • Neuroblastoma
  • Wilms tumour
  • Lymphoma (including both Hodgkin and non-Hodgkin)
  • Rhabdomyosarcoma
  • Retinoblastoma
  • Bone cancer (including osteosarcoma and Ewing sarcoma)

Other types of cancers are rare in children, but they do happen sometimes. In very rare cases, children may even develop cancers that are much more common in adults. 


Leukemias, which are cancers of the bone marrow and blood, are the most common childhood cancers. They account for about 30% of all cancers in children. The most common types in children are acute lymphocytic leukaemia (ALL) and acute myelogenous leukaemia (AML). 


Brain and spinal cord tumours

Brain and central nervous system tumours are the second most common cancers in children, making up about 26% of childhood cancers. There are many types of brain tumours. 



Neuroblastoma starts in early forms of nerve cells found in a developing embryo or fetus. About 6% of childhood cancers are neuroblastomas. This type of cancer develops in infants and young children. It is rarely found in children older than 10. 


Wilms tumour

Wilms tumour (also called nephroblastoma) starts in one, or rarely, both kidneys. It is most often found in children about 3 to 4 years old, and is uncommon in children older than age 6. 



Lymphomas start in immune system cells called lymphocytes. They most often start in lymph nodes and other lymph tissues, like the tonsils or thymus. These cancers can also affect the bone marrow and other organs.

Hodgkin lymphoma, accounts for about 3% of childhood cancers. It is more common, though, in early adulthood (age 15 to 40, usually people in their 20s) and late adulthood (after age 55). Hodgkin lymphoma is rare in children younger than 5 years of age.

Non-Hodgkin lymphoma, makes up about 5% of childhood cancers. It is more likely to occur in younger children than Hodgkin lymphoma, but it is still rare in children younger than 3. These cancers often grow quickly and require intensive treatment. 



Rhabdomyosarcoma starts in cells that normally develop into skeletal muscles. (These are the muscles that we control to move parts of our body.) This type of cancer can start nearly any place in the body, including the head and neck, groin, belly (abdomen), pelvis, or in an arm or leg.



Retinoblastoma is a cancer of the eye. It accounts for about 2% of childhood cancers. It usually occurs in children around the age of 2, and is seldom found in children older than 6. Retinoblastomas are usually found because a parent or doctor notices a child’s eye looks unusual. Normally when you shine a light in a child’s eye, the pupil (the dark spot in the centre of the eye) looks red because of the blood in vessels in the back of the eye. In an eye with retinoblastoma, the pupil often looks white or pink. This white glare of the eye may be noticed after a flash picture is taken.


Bone cancers

Cancers that start in the bones (primary bone cancers) occur most often in older children and teens, but they can develop at any age. They account for about 3% of childhood cancers.

Two main types of primary bone cancers occur in children:

Osteosarcomais most common in teens, and usually develops in areas where the bone is growing quickly, such as near the ends of the long bones in the legs or arms.

Ewing sarcoma is a less common type of bone cancer, which can also cause bone pain and swelling. It is most often found in young teens


Professor David Reynders

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