Sentinel lymph node biopsy (SLNB) is a surgical procedure performed to determine if a cancer has spread from a primary tumor into the lymphatic system.
A lymph node is part of the body's lymphatic system, a network of lymph vessels that carries clear fluid called lymph. The lymphatic system circulates the protein-rich lymph fluid throughout the body. 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.
The sentinel lymph node (SLN) 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 may be more than one sentinel lymph node.
In SLN biopsy, the surgeon removes and examines the sentinel lymph node for cancer. This technique is used to stage certain types of cancer. Staging is focused on determining the severity of the disease. 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 surgeon determine the stage (severity and spread) of the cancer and develop an appropriate treatment plan.
Sentinel node biopsy is most frequently used in breast cancer and melanoma. It may also be relevant in staging other cancers including vulvar cancer, cervical cancer, endometrial cancer, prostate cancer, squamous head and neck cancer, thyroid cancer, non-small cell lung cancer, and Merkel cell carcinoma.
A procedure called lymphatic mapping or lymphoscintigraphy is performed that maps the way lymph drains from the tumor to the lymph nodes. The surgeon injects a radioactive substance, blue dye, or both near the tumor. A scanner is then used to find the sentinel lymph nodes containing the radioactive substance or the lymph nodes stained with dye. Once the SLN is located, the surgeon makes a small incision (about ½ inch) in the skin overlying the SLN and removes the lymph nodes.
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.
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 do not generally need not 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.
For melanoma patients, SLN biopsy is low-risk procedure that helps to identify high-risk patients who might benefit from more aggressive therapy, such as selective or complete lymphadenectomy or adjuvant interferon alfa-2b.
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.