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I have melanoma! Why do I need a sentinel lymph node biopsy?

Lymph system: We have lymph nodes, which are connected by lymph vessels (shown in green), throughout our body. The largest number of lymph nodes are found in our neck, armpits, and groin.

Melanoma is a type of skin cancer that can spread quickly. When melanoma starts to spread, it often travels to a lymph node near the melanoma first.

Having a sentinel lymph node biopsy (SLNB) can tell whether cancer cells have spread to a nearby lymph node. If the cancer has spread to a lymph node, you have stage III melanoma. Knowing the stage of your cancer helps your doctors create an appropriate treatment plan for you.

What exactly is a SLNB?

It’s a type of surgery that’s performed in an operating room. During this surgery, the surgeon makes a small incision and removes one or a few lymph nodes. These nodes are tested to see if they contain cancer cells.

When would a doctor recommend a SLNB?

Your doctor may recommend a SLNB if you have an increased risk of melanoma spreading to a lymph node. Melanoma has a greater risk of spreading to the nearest lymph nodes when it:

A doctor can tell if melanoma has any of these risks by reading your biopsy report.

A SNLB is only recommended when you have a high risk of melanoma spreading and your doctor did not feel any enlarged lymph nodes when examining you.

If your doctor felt any enlarged lymph nodes, you need different testing.

When would a patient have a SLNB?

Most patients have a SLNB when they have their melanoma surgery.

The melanoma surgery differs from the skin biopsy. You had a skin biopsy when your dermatologist (or another doctor) removed what looked like a melanoma from your skin.

For patients with melanoma, the next step after a skin biopsy is usually melanoma surgery. During melanoma surgery, the goal is to remove any remaining cancer. If your melanoma is thin, your dermatologist may perform the melanoma surgery in a medical office or surgical suite while you are awake.

Patients who have an early, thin melanoma do not need to have a SLNB.

If the melanoma is thick or has spread, you may be treated in an operating room. A SLNB is also performed in an operating room.

What happens during a SLNB?

A SLNB begins with finding the sentinel lymph node(s). This is the first lymph node(s) that cancer cells are likely to reach. You’ll be awake during this part.

To find your sentinel lymph node(s), you may receive an injection of a radioactive solution or blue dye. Some surgeons prefer to use both, so you’ll receive 2 injections.

If your surgeon wants to use a radioactive solution, you’ll receive the injection hours before the surgery — or even the day before. The dye, which stains your sentinel lymph nodes blue, is injected right before the surgery.

Just before the surgery to remove the sentinel lymph node(s), you’ll receive anesthetic that puts you to sleep.

In the operating room, your surgeon first needs to find your sentinel nodes. If you received a radioactive solution, your surgeon uses a handheld device called a gamma detector to find the radioactive lymph nodes. If dye was injected, your surgeon looks for the blue lymph nodes. Once found, your surgeon removes the radioactive (or blue) lymph nodes. These will be sent to a lab where they can be examined for cancer cells.

While you are in the operating room, you may also have melanoma surgery.

After the surgery(ies), you will be moved to a recovery room, where you’ll be watched. Many patients go home the same day. Some need to spend the night in the hospital.

What happens if cancer cells are found?

If cancer cells are found in the removed lymph nodes, your melanoma stage changes. Once the cancer travels to nearby lymph nodes, it is a stage III melanoma.

If you have stage III melanoma, your doctor will talk with you about your treatment options.

Are there any risks in having a SLNB?

Every surgery has risks. After a SLNB, you may have numbness, pain, or bruising where the lymph node(s) was removed. You may also have a buildup of fluid in the area. Sometimes, the skin in the area where you had the SLNB feels hard or thick. This can make it difficult to move that part of your body. These side effects tend to be temporary.

Some patients have an allergic reaction to the blue dye. A few patients have developed a life-threatening allergic reaction.

If you have any allergies, tell your doctors before having a SLNB.

With any surgery, you can develop an infection. Following the instructions given to you after the surgery can reduce this risk.

SLNB tells you one thing

A SLNB can only tell you whether cancer cells have spread to the lymph nodes nearest the melanoma. This is where melanoma usually travels to first when it starts to spread. A SLNB cannot tell you whether cancer cells have spread elsewhere.

Ultimately, the decision about whether to have a SLNB is up to you. Your doctor can help you decide by answering your questions.


Cooper C, Wayne JD, et al. “A 10-year, single-institution analysis of clinicopathologic features and sentinel lymph node biopsy in thin melanomas.” J Am Acad Dermatol. 2013;69(5):693-9.

Faries MB, Cochran AJ, et al. “Multicenter Selective Lymphadenectomy Trial-I confirms the central role of sentinel node biopsy in contemporary melanoma management.” Br J Dermatol. 2015;172(3):571-3.

Gerami P, cook RW, et al. “Gene expression profiling for molecular staging of cutaneous melanoma in patients undergoing sentinel lymph node biopsy.” J Am Acad Dermatol. 2015;72(5):780-5.

Leung AM, Morton DL, et al. “Staging of regional lymph nodes in melanoma: a case for including non-sentinel lymph node positivity in the American Joint Committee on Cancer staging system.” JAMA Surg. 2013;148(9):879-84.

Liang MI and Carson WE. “Biphasic anaphylactic reaction to blue dye during sentinel lymph node biopsy.” World J Surg Oncol. 2008;6:79.

Lima Sánchez J, Sánchez Medina M, et al. “Sentinel lymph node biopsy for cutaneous melanoma: a 6-years study.” Indian J Plast Surg. 2013;46(1):92-7.

Morton DL, Thompson JF, et al. “Final trial report of sentinel-node biopsy versus nodal observation in melanoma.” N Engl J Med. 2014;370(7):599-609.

Wat H, Senthilselvan A, et al. “A retrospective, multicenter analysis of the predictive value of mitotic rate for sentinel lymph node (SLN) positivity in thin melanomas.” J Am Acad Dermatol. 2016;74(1):94-101

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