What does benign mean?
In pathology, benign is used to describe a non-cancerous growth such as a tumour. It can also be used to describe normal tissue. The opposite of benign is malignant.
A benign tumour is a large group of non-cancerous cells that are growing faster than the normal cells around them. Because they are growing faster than the normal cells, the tumour cells form a mass that stands out from the surrounding tissue.
While benign tumours can still cause damage by compressing nearby structures, such as other organs, nerves, or blood vessels, the cells cannot typically spread to other parts of the body. The movement of tumour cells to another part of the body is called metastasis and this is usually only seen with malignant (cancerous) tumours.
How do pathologists decide if a tumour is benign?
One of the most important decisions a pathologist has to make every day is deciding whether a tumour is benign or malignant. To help them make this decision, pathologists examine a sample of the tumour under the microscope and look for the following features:
- The types of cells inside the tumour.
- The shape, size, and colour of the tumour cells. Very abnormal looking or atypical cells are more often found in malignant tumours.
- Tumour cells that are dividing to create new tumour cells. This process is called mitoses. Benign tumours tend to have very few dividing cells although some types are allowed to have many.
- The relationship between the tumour and the surrounding tissue. Most benign tumours are clearly separated from the surrounding normal tissue.
- The presence of perineural or lymphovascular invasion. Both of these features are rarely seen in benign tumours.