Types of kidney tumours in children
Wilms tumour is a cancerous (malignant) tumour of the kidney that can grow into and destroy nearby tissue. It can also spread (metastasize) to other parts of the body. Wilms tumour is the most common type of cancerous kidney tumour in children. Other cancerous kidney tumours can also develop in children, but they are less common.
Wilms tumour develops when a mistake happens in an immature (embryonic) kidney cell. This mistake means the cell doesn’t develop normally to become a mature kidney cell. It causes the cell, and the cells it produces, to multiply and grow out of control. These cells eventually form a tumour, which is called Wilms tumour.
Wilms tumour can be divided into 2 types based on how it looks under a microscope (called histology). Doctors tell them apart based on whether anaplasia is present. Anaplasia is a loss of differentiation in cells so that they return to a less specialized or immature form.
About 90% of Wilms tumours are classified as having a favourable histology. There is no anaplasia present.
Wilms tumours with a favourable histology respond better to chemotherapy, so children with these tumours generally have a better prognosis than those with an anaplastic histology.
About 5% to 10% of Wilms tumours are classified as anaplastic histology. Anaplastic histology may also be called unfavourable histology. The cells in these tumours look very different from normal kidney cells and divide abnormally.
Anaplasia may be focal or diffuse. With focal anaplasia, there is one or a few very localized regions of anaplasia in the tumour. The rest of the tumour looks like a regular Wilms tumour. With diffuse anaplasia, anaplasia is found throughout the tumour.
Anaplastic tumours are more difficult to treat because they tend to be more resistant to chemotherapy. Anaplastic tumours are more likely to recur than tumours with a favourable histology.
Rare kidney tumours
The following kidney tumours in children are rare.
Mesoblastic nephroma is usually a non-cancerous kidney tumour that occurs in the first few months of life. It is usually cured with surgery, but sometimes chemotherapy is given. These tumours sometimes come back soon after treatment so close follow-up is important in the first year.
Clear cell sarcoma of the kidney is much more likely than Wilms tumour to spread to other parts of the body. It is also harder to treat. It may spread to the lungs, bone, brain and soft tissues. Treatment is similar to treatment for more advanced stages of Wilms tumour. It may include removal of the kidney (nephrectomy) along with nearby lymph nodes, followed by radiation therapy and a combination of chemotherapy drugs.
Rhabdoid tumour of the kidney occurs most often in infants and young children. It is very aggressive and most children are diagnosed with advanced cancer. It often spreads to the brain and lungs. There is no standard treatment for rhabdoid tumour. Treatment usually involves a combination of chemotherapy drugs, with or without radiation therapy.
Renal cell carcinoma develops most often in young people 15 to 19 years old. Treatment usually involves surgery. Immunotherapy may be used to treat advanced renal cell carcinoma.
Other sarcomas of the kidney are rare but can occur at any age. They are usually treated with a combination of surgery, radiation and chemotherapy.
The normal process by which immature (unspecialized) cells develop individual characteristics to become mature (specialized) cells.
Differentiation is used to describe the extent to which cancerous cells resemble normal cells. Differentiated cancer cells look and act like normal cells; they tend to grow and spread slowly. Undifferentiated cancer cells do not look or act like normal cells; they tend to grow and spread quickly.