How is a biopsy done?

A biopsy sample is taken in one of three ways: with a needle, through an endoscope, or during surgery. Which one you get depends on where the abnormal area sits and how much tissue the pathologist needs.

The National Cancer Institute describes each route.

With a needle, the doctor withdraws tissue or fluid. This method is used for bone marrow aspirations, spinal taps, and some breast, prostate, and liver biopsies. With endoscopy, a thin, lighted tube is inserted through a natural body opening such as the mouth or the anus. A colonoscopy and a bronchoscopy both work this way. With surgery, a surgeon removes the abnormal area during an operation. An excisional biopsy takes the entire area of abnormal cells, often with a rim of normal tissue around it. An incisional biopsy takes only part of the abnormal area.

Some biopsies require a sedative or anesthesia. Local anesthesia numbs one small area. Regional anesthesia numbs a whole part of the body, such as an arm or a leg. General anesthesia causes a complete loss of awareness, like a very deep sleep. Many needle biopsies need nothing more than a local injection and take a few minutes.

One kind of biopsy is worth knowing by name. In a sentinel lymph node biopsy, the surgeon injects a radioactive substance, a blue dye, or both near the tumor. The team then tracks which lymph node the material reaches first, since that node is the one cancer would most likely reach first too. A small cut removes it for examination. A negative result can spare you a larger operation to take out many nodes. The risks include swelling called lymphedema, a fluid pocket called a seroma, numbness or tingling, trouble moving the limb, and an allergic reaction to the blue dye.

After the sample leaves the room, a pathologist examines it under a microscope and runs other tests on the cells. The findings go into a pathology report. That report typically holds a gross description of what the tissue looked like to the naked eye, a microscopic description, and a final diagnosis. It also states the margins. Margins are called negative or clean when no cancer cells sit at the edge of the removed tissue, and positive or involved when cancer cells do. Some added tests, such as fluorescence in situ hybridization or karyotyping, look for genetic changes and take longer to come back. That is why results often arrive in stages rather than all at once.

A biopsy answers a question about the tissue that was taken, and only that tissue. NCI names the false negative as a known outcome of sentinel node biopsy, meaning cancer was not found in the node even though it had spread. The same logic applies elsewhere. If a report comes back nondiagnostic or insufficient, the sample did not contain enough usable tissue, and the test may need repeating. If a benign result does not match a scan that looked worrying, your team may repeat it rather than accept the mismatch.

Your care team can explain which method is best for your situation. Before the procedure, ask whether you will be awake, and whether any of your medicines, especially blood thinners, should be stopped first. Afterward, ask when results are expected and who will call you. Request a copy of the pathology report for your own file. Every treatment decision that follows is built on that one document.