This is a definitive test to diagnose cancer. A biopsy involves the removal of a piece of tissue for examination under a microscope to see if cancer is present.Today, many of these procedures can be done by extracting small amounts of tissue from the body via a needle inserted through the skin and into a growth that cannot be felt or viewed by an imaging procedure, such as MRI, X–ray, etc.

For example, when breast cancer is suspected, doctors may be able to do biopsy of a lump that can be felt or one that shows up on a mammogram by inserting needles into the suspicious growth.These are called “Stereotactic” biopsies because in order to get an adequate sampling of cells several needles may have to be inserted from various angles.A similar procedure is used to extract cells from suspicious thyroid nodules that could be malignant. Other biopsies can be done via a “Scope” or flexible tube inserted into the body (see endoscopy).