Canadian Cancer Society logo
You are here: 

Types of tumours

Tumours are groups of abnormal cells that form lumps or growths. Different types of tumours grow and behave differently, depending on whether they are non-cancerous (benign) or cancerous (malignant). Precancerous conditions have the potential to develop into cancer.

Benign tumours

Benign tumours are non-cancerous. They rarely cause serious problems or threaten life unless they occur in a vital organ or grow very large and press on nearby tissues.

Benign tumours tend to grow slowly and stay in one place, not spreading into other parts of the body.

Once removed by surgery, benign tumours don’t usually come back (recur). Benign tumours usually stay non-cancerous, except in very rare cases.

Back to top

Precancerous conditions

Precancerous (premalignant) cells are abnormal cells that may develop into cancer if they aren’t treated. Some cells develop mild changes that may disappear without any treatment. Other cells pass on genetic changes and new cells gradually become more and more abnormal until they turn into cancer. It can take a long time for this to happen.

Precancerous (or premalignant) changes can vary in their degree of abnormality.

  • hyperplasia – an abnormal increase in the number of cells
    • Some hyperplasias are precancerous, but most are not.
  • atypia (atypical) – cells look slightly abnormal under a microscope
    • Sometimes atypia refers to changes caused by healing and inflammation, rather than a precancerous change, and the cells go back to normal once inflammation goes away or the body heals.
  • metaplasia – cells look normal under a microscope, but are not the type normally found in the that tissue or area
    • Metaplasias are usually not precancerous.
  • dysplasia – cells develop abnormally, have an abnormal appearance and are not organized like normal cells
    • Dysplasia almost always refers to a precancerous condition.

People with precancerous conditions are usually checked regularly, so they can be treated quickly if cell changes become more severe.

Back to top

Malignant tumours

Malignant tumours are cancerous. Cancer can start in any one of the millions of cells in our bodies. Cancer cells have a larger nucleusnucleusThe part of the cell that holds the chromosomes, which contain DNA (genetic information). that looks different from a normal cell’s nucleus, and cancer cells behave, grow and function quite differently from normal cells.

Malignant tumours vary in size and shape. They grow in an uncontrolled, abnormal way and can grow into (invade) nearby tissues, blood vessels or lymphatic vessels. They can interfere with body functions and become life-threatening.

Cancer cells can break off and spread to distant locations in the body (metastasize). Cancer that spreads from its original location (the primary tumour) to a new part of the body is called metastatic cancer. Malignant tumours can also come back (recur) after they are removed.

Back to top

How tumours and cancers are named

The most common way to name cancers is to do so according to the place in the body they start, such as breast cancer or prostate cancer. Cancers of the blood are called leukemia, while cancer of the plasma cells is called multiple myeloma and cancers of the lymphatic system are called lymphoma. Some cancers have been named after the person who first described them (for example, Hodgkin lymphoma or Wilms’ tumour).

Another way to name some benign or malignant tumours is after the type of cell or tissue it develops from (tissue of origin). Most benign tumours and some malignant tumours have the suffix "–oma" at the end of their name. When a malignant tumour has the same name as a benign tumour, the word "carcinoma" or "sarcoma" is added to the end to identify it as cancer. For example, a benign tumour of fatty tissue is called a lipoma, whereas a malignant tumour of fatty tissue is called a liposarcoma.

Back to top


Photo of Claude Perreault Dr Perreault identified new molecules that may help make immunotherapies work for more people.

Read more

Advocating for cancer patients

Illustration of a bullhorn

Our staff and volunteers meet with elected officials from local, provincial and national governments to persuade them to make the fight against cancer one of their top priorities.

Learn more