by Jason Wasserman MD PhD FRCPC
May 1, 2022

What is a biopsy?

A biopsy is a minor surgical procedure performed to remove a small piece of tissue from the body. The tissue sample is then sent to a pathologist for examination under the microscope.

This picture shows how a type of biopsy called a core needle biopsy is performed.

What is the purpose of a biopsy?

A biopsy is typically performed on an area of the body that appears abnormal and the goal of the biopsy is to provide an explanation or cause for the abnormality. In medicine, this is called a diagnosis. For example, a female patient with a ‘lump’ in her breast may undergo a biopsy of the lump in order to determine if the lump is non-cancerous or cancerous. Or a patient with stomach pain may undergo a stomach biopsy to see if the pathologist can see any condition or disease under the microscope that could explain the pain. In both cases, only a very small piece of tissue is removed and sent for pathological examination.

Biopsies can also be performed to monitor the status of a known disease or to see if a treatment has been successful. For example, a patient with Crohn’s disease will undergo biopsies at regular intervals to monitor the status of the disease. Alternatively, a patient with breast cancer may undergo a biopsy after receiving chemotherapy to see if there is any cancer remaining in the breast.

What are the limitations of a biopsy?

Biopsies are not usually performed to remove an entire area of abnormal tissue or to cure a patient of a disease. For example, a biopsy performed on a patient with a ‘lump’ in their breast will usually not remove the entire lump. The biopsy is simply performed to provide a diagnosis. A more extensive surgical procedure, either an excision or a resection, would be performed to remove the entire lump.

Because a biopsy only provides information about the small piece of tissue sampled, it is always possible that some of the tissue not sampled contains important information that would change the diagnosis. For this reason, pathologists will only make a diagnosis based on what they can see in the sample of tissue provided to them.

In some cases, this will mean that the pathologist will only provide a partial diagnosis. For example, a biopsy performed on a large tumour may only provide a diagnosis of cancer without specifying the exact type of cancer present. When the entire tumour is removed, all of the tissue will be examined and a complete or final diagnosis will be provided.

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