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The Skin Cancer Biopsy: What You Need to Know

Guide to How Skin Cancer is Diagnosed with a Skin Biopsy

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Updated May 01, 2009

If your doctor thinks that a lesion on your skin might be cancerous, he or she will take a sample from the suspicious area for examination under a microscope. This is called a skin biopsy, which is then used to plan a treatment strategy appropriate for the cancer type (nonmelanoma or melanoma). Different methods can be used, and the choice depends on the size of the affected area, the type of suspected cancer, and its location on your body.

Skin biopsies are done using a local anesthetic (numbing medicine), which is injected into the area with a small needle. You will likely feel a small pinch and a little stinging as the medicine is injected, but you should not feel any pain during the biopsy. Any biopsy is likely to leave a scar. Since different methods produce different types of scars, you should ask the doctor about biopsies and scarring before the procedure is done.

Shave biopsy

After the injection of anesthetic, the doctor "shaves" off the top layers of the skin (the epidermis and the outer part of the dermis) with a surgical blade. A shave biopsy is useful in diagnosing basal cell or squamous cell skin cancers and in sampling moles when the risk of melanoma is very low. It is not generally recommended if a melanoma is suspected because a shave biopsy sample may not be thick enough to measure how deeply the melanoma has invaded the skin.

Punch biopsy

A punch biopsy removes a deeper sample of skin but is more limited in the diameter of the sample that can be taken. The doctor uses a tool that looks like a tiny round cookie cutter. Once the skin is numbed with a local anesthetic, the doctor rotates the punch biopsy tool on the surface of the skin until it cuts through all the layers of the skin, including the dermis, epidermis, and the upper parts of the subcutis.

Incisional and excisional biopsies

If the doctor has to examine a tumor that may have grown into deeper layers of the skin, he or she will use an incisional or excisional biopsy technique. Incisional biopsy involves removing only a portion of the tumor. Removal of the entire tumor is called an excisional biopsy, and is done when melanoma is suspected. In this case, a surgical knife is used to cut through the full thickness of skin. A wedge or ellipse of skin is removed for further examination, and the edges of the wound are then sutured together. Both of these types of biopsies can be done using local anesthesia.

Examining the biopsy samples

In order to make a diagnosis, all skin biopsy samples are looked at under a microscope. The skin sample is sent to a pathologist, a doctor who has been specially trained in the microscopic examination and diagnosis of tissue samples. Often, the sample is sent to a dermatopathologist, a doctor who has special training in making diagnoses from skin samples.

Lymph node biopsy

If your doctor feels lymph nodes that are too large and/or too firm, a lymph node biopsy may be done to determine whether cancer has spread from the skin to the lymph nodes. In addition, special tests can be done on the biopsy sample that can tell whether it is a melanoma or some other kind of cancer.

Fine needle aspiration

A fine needle aspiration (FNA) biopsy uses a syringe with a thin needle to remove small tissue fragments from a tumor. The needle is smaller than the needle used for a blood test. A local anesthetic is sometimes used to numb the area. This test rarely causes much discomfort and does not leave a scar. An FNA biopsy is not used to diagnose a suspicious skin tumor, but it may be used to biopsy large lymph nodes near a skin cancer to find out if the cancer has spread to them.

Sentinel lymph node mapping and biopsy

This has become a common procedure to determine if melanoma has spread to the lymph nodes. This procedure can find the lymph nodes that drain lymph fluid from the area of the skin where the melanoma started. If the melanoma has spread, these lymph nodes are usually the first place it will go. That is why these lymph nodes are called sentinel nodes (they stand sentinel, or watch, over the tumor, so to speak).

To map the sentinel lymph node (or nodes), some time before surgery the doctor injects a small amount of radioactive material and usually a blue dye into the area of the melanoma. By checking various lymph node areas with a radioactivity detector (which works like a Geiger counter), the doctor can see what group of lymph nodes the melanoma is most likely to travel to. The surgeon makes a small incision in the identified lymph node area. The lymph nodes are then checked to find which one(s) turned blue or became radioactive. When the sentinel node has been found, it is removed and looked at under a microscope. If the sentinel node does not contain melanoma cells, no more lymph node surgery is needed because it is unlikely the melanoma would have spread beyond this point. If melanoma cells are found in the sentinel node, the remaining lymph nodes in this area are removed and looked at as well. This is known as a lymph node dissection. If a lymph node near a melanoma is abnormally large, the sentinel node procedure may not be needed. The enlarged node is then biopsied.

Sources:

"How Is Squamous and Basal Cell Skin Cancer Diagnosed?" American Cancer Society. June 2008. 15 October 2008.

"How Is Melanoma Diagnosed?" American Cancer Society. June 2008. 15 October 2008.

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