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Sentinel Lymph Node Biopsy: Questions and Answers 

1. What is a lymph node? 

A lymph node is part of the body’s lymphatic system. In the lymphatic system, a 

network of lymph vessels carries clear fluid called lymph. Lymph vessels lead to lymph 

nodes, which are small, round organs that trap cancer cells, bacteria, or other harmful 

substances that may be in the lymph. Groups of lymph nodes are found in the neck, 

underarms, chest, abdomen, and groin. 

2. What is a sentinel lymph node (SLN)? 

The sentinel lymph node is the first lymph node to which cancer is likely to spread from 

the primary tumor. Cancer cells may appear in the sentinel node before spreading to 

other lymph nodes. In some cases, there can be more than one sentinel lymph node. 

3. What is SLN biopsy? 

SLN biopsy is a procedure in which the sentinel lymph node is removed and examined 

under a microscope to determine whether cancer cells are present. SLN biopsy is based 

Key Points 

• A sentinel lymph node (SLN) is the first lymph node(s) to which cancer 

cells are likely to spread from the primary tumor. Cancer cells may 

appear in the sentinel node before spreading to other lymph nodes 

(see Question 2). 

• SLN biopsy can be used to help determine the extent or stage of cancer 

(see Question 3). 

• Because SLN biopsy involves the removal of fewer lymph nodes than 

standard lymph node removal procedures, the potential for side effects is 

lower (see Questions 5 and 6). 
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on the idea that cancer cells spread (metastasize) in an orderly way from the primary 

tumor to the sentinel lymph node(s), then to other nearby lymph nodes (1, 2). 

A negative SLN biopsy result suggests that cancer has not spread to the lymph nodes. A 

positive result indicates that cancer is present in the SLN and may be present in other 

lymph nodes in the same area (regional lymph nodes). This information may help the 

doctor determine the stage of cancer (extent of the disease within the body) and develop 

an appropriate treatment plan (2). 

4. What happens during the SLN biopsy procedure? 

In SLN biopsy, one or a few lymph nodes (the sentinel node or nodes) are removed. To 

identify the sentinel lymph node(s), the surgeon injects a radioactive substance, blue dye, 

or both near the tumor. The surgeon then uses a scanner to find the sentinel lymph 

nodes(s) containing the radioactive substance or looks for the lymph node(s) stained with 

dye. Once the SLN is located, the surgeon makes a small incision (about 1⁄2 inch) in the 

skin overlying the SLN and removes the lymph node(s). 

The sentinel node(s) is/are checked for the presence of cancer cells by a pathologist (a 

doctor who identifies diseases by studying cells and tissue under a microscope). If cancer 

is found, the surgeon will usually remove more lymph nodes during the biopsy procedure 

or during a follow-up surgical procedure. SLN biopsy may be done on an outpatient 

basis or require a short stay in the hospital. 

5. What are the possible benefits of SLN biopsy?

To understand the possible benefits of SLN biopsy, it helps to know about standard 

lymph node removal. Standard lymph node removal involves surgery to remove most of 

the lymph nodes in the area of the tumor (regional lymph nodes). For example, breast 

cancer surgery may include removing most of the axillary lymph nodes, the group of 

lymph nodes under the arm. This is called axillary lymph node dissection (ALND). 

If SLN biopsy is done and the sentinel node does not contain cancer cells, the rest of the 

regional lymph nodes may not need to be removed. Because fewer lymph nodes are 

removed, there may be fewer side effects. When multiple regional lymph nodes are 

removed, the patient may experience side effects such as lymphedema (swelling caused 

by excess fluid build-up), numbness, a persistent burning sensation, infection, and 

difficulty moving the affected body area (1, 3). 

6. What are the side effects and disadvantages of SLN biopsy?

Side effects of SLN biopsy can include pain or bruising at the biopsy site and the rare 

possibility of an allergic reaction to the blue dye used to find the sentinel node. Patients 

may find that their urine is discolored or that their skin has been stained the same color as 

the dye. These problems are temporary (2). 
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Although some surgeons consider SLN biopsy to be the standard of care for some 

cancers, its role and benefit are yet to be determined (2). We do not know whether SLN 

biopsy improves a patient’s survival or reduces the chance that the cancer will recur 

(come back). That is why studies are being conducted to compare SLN biopsy with 

standard lymph node dissection (see Question 8). 

7. What research has been done with SLN biopsy?

The concept of mapping (finding) the SLN was first reported in 1977 by a researcher 

studying cancer of the penis (2, 3, 4). In the 1980s, researchers at the University of 

California, Los Angeles (UCLA) developed the technique of lymphatic mapping to 

identify the SLN in patients with melanoma (3). SLN mapping for breast cancer was first 

reported in 1994 (1, 3). Since then, researchers have improved methods for finding the 

SLN. Several studies have shown that when the sentinel node is negative, the remaining 

nodes are usually negative (1, 3). However, these studies were done in a small number of 

centers and overall survival was not examined. 

Other research has focused on the identification of the SLN in patients with cancer of the 

vulva, cervix, prostate, bladder, thyroid, head and neck, colon, rectum, stomach, as well 

as non-small-cell lung cancer and Merkel cell cancer (2, 3, 4, 5). Clinical studies 

continue to examine the accuracy of SLN biopsy and its effect on survival of people with 

various cancers. 

8. What clinical trials (research studies) are being conducted with SLN biopsy?

The National Cancer Institute (NCI) recently sponsored two large randomized clinical 

trials (research studies) for breast cancer comparing SLN biopsy with conventional 

axillary lymph node dissection. The trials were conducted by the National Surgical 

Adjuvant Breast and Bowel Project (NSABP) and the American College of Surgeons 

Oncology Group (ACOSOG). NSABP and ACOSOG are both NCI-sponsored Clinical 

Trials Cooperative Groups, which are networks of institutions and physicians across the 

country who jointly conduct trials. Although several studies have examined the 

correlation between the sentinel node and the remaining axillary nodes, these are the first 

two randomized trials that will compare the long-term results of SLN removal with full 

axillary node dissection. Both of these large trials are now closed. 

9. Where can people find more information about clinical trials with SLN biopsy?

The NCI’s Web site provides general information about clinical trials at 

http://www.cancer.gov/clinicaltrials/ on the Internet. It also links to PDQ®, the NCI’s 

cancer information database. PDQ contains detailed information about specific ongoing 

clinical trials in the United States, Europe, and elsewhere. 

Information about clinical trials with SLN biopsy is also available from the NCI’s Cancer 

Information Service (CIS). The CIS, a national information and education network, is a 

free public service of the NCI, the Nation’s primary agency for cancer research. The 
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toll-free phone number for the CIS is 1–800–4–CANCER (1–800–422–6237). For 

callers with TTY equipment, the number is 1–800–332–8615. The CIS also offers online 

assistance through the Help link at http://www.cancer.gov/ on the Internet. 

Selected References 

1. Harris JR, Lippman ME, Morrow M, Osborne CK, editors. Diseases of the Breast. 

3rd ed. Philadelphia: Lippincott Williams & Wilkins, 2004. 

2. DeVita VT Jr., Hellman S, Rosenberg SA, editors. Cancer: Principles and Practice of 

Oncology. Vol. 1 and 2. 6th ed. Philadelphia: Lippincott Williams and Wilkins, 2001. 

3. Cochran AJ, Roberts AA, Saida T. The place of lymphatic mapping and sentinel node 

biopsy in oncology. International Journal of Clinical Oncology 2003; 8:139–150. 

4. Gipponi M, Solari N, Di Somma FC, Bertoglio S, Cafiero F. New fields of application of 

the sentinel lymph node biopsy in the pathologic staging of solid neoplasms: Review of 

literature and surgical perspectives. Journal of Surgical Oncology 2004; 85:171–179. 

5. Ota DM. What’s new in general surgery: Surgical oncology. Journal of the American 

College of Surgeons 2003; 196(6):926–932. 

# # # 

Related Resources

Publications (available at http://www.cancer.gov/publications) 

• National Cancer Institute Fact Sheet 1.4, NCI’s Clinical Trials Cooperative Group 

Program

• National Cancer Institute Fact Sheet 5.14, Improving Methods for Breast Cancer 

Detection and Diagnosis

• National Cancer Institute Fact Sheet 5.32, Staging: Questions and Answers

• National Cancer Institute Fact Sheet 7.47, How To Find a Doctor or Treatment 

Facility If You Have Cancer

National Cancer Institute (NCI) Resources

Cancer Information Service (toll-free)

 Telephone: 1–800–4–CANCER (1–800–422–6237) 

 TTY: 1–800–332–8615 
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Online 

NCI’s Web site: http://www.cancer.gov 

LiveHelp, NCI’s live online assistance: 

https://cissecure.nci.nih.gov/livehelp/welcome.asp

This fact sheet was reviewed on 4/27/05