Sentinel lymph node biopsy
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Purpose of a sentinel lymph node biopsy
Merkel cell carcinoma Merkel cell carcinoma A skin cancer composed of cells that look microscopically similar to normal Merkel cells present in the skin. MCC was first described in 1972 and only in the 1990s was the CK20 antibody developed to make it easily identifiable by pathologists. Many doctors and patients are not aware of this cancer because of its recent description and relative rarity (~2,000 cases/year in the US--roughly 30 times less common than melanoma). About 40% of patients treated for MCC will experience a recurrence, making it far more aggressive than most other types of skin cancer, including melanoma. can travel from the skin, through the lymphatic vessels lymphatic vessels Thin tubes that carry lymph (also called lymphatic fluid) including white blood cells through the lymphatic system to lymph nodes and eventually back into the bloodstream. Lymphatic vessels originate in the tissues of the body like blood vessels. , to the sentinel lymph node lymph node A rounded mass of lymphatic tissue that is usually surrounded by connective tissue and about the size of a green pea. Lymph nodes filter lymphatic fluid, also know as lymph, which is fluid that drains from the tissues of the body and contains immune cells. Cancer cells often travel through lymph vessels and lodge and grow in lymph nodes, sometimes causing the nodes to markedly increase in size. . The sentinel lymph node is the first lymph node that connects with the part of the body where the cancer cancer A term used to describe diseases in which abnormal cells continually divide without normal regulation. Cancerous cells may invade surrounding tissues and may spread to other regions of the body via blood and the lymphatic system. arose. If a lymph node feels enlarged, it may contain MCC (macrometastases). Sometimes, lymph nodes may contain MCC, but not feel enlarged (micrometastases). Lymph nodes should be removed (biopsied) to determine if MCC is present.
There is a technique to identify the sentinel lymph node when it cannot be felt on physical exam physical exam Process of evaluating the body through the use of observation or palpation (feeling with hands). . A blue dye and or a radioactive tracer are injected at the site of the primary lesion primary lesion The abnormal tissue that appeared first. The majority of Merkel cell carcinoma primary lesions occur in sun-exposed areas. In some cases of MCC (approximately 11%) the patient has no primary lesion and instead has a nodal presentation (disease in a lymph node only). In these cases the primary lesion likely was destroyed by the immune system. . Within 5 to 10 minutes, the dye and tracer travel along the same path that cancer cells would spread through the lymphatic vessels and collect in the sentinel lymph node. An instrument that detects the tracer is used to map the path from the skin to the sentinel lymph node. The sentinel lymph node is removed and examined for the presence of MCC under a microscope. If MCC is not found in the sentinel lymph node, then the chance that it has spread elsewhere in the body is lower than if micrometastases are present.
This technique has a low risk of significant side effects, provides useful information on the chance of spread, and identifies the lymph node region containing the sentinel lymph node ( draining lymph node draining lymph node The particular lymph node(s) to which the lymph fluid from an area of tissue flows. basin), which is sometimes difficult, especially for lesions on the trunk.
A Closer Look
One third of MCC patients whose lymph nodes feel normal to the patient and their doctor in fact already have microscopic spread of MCC to the sentinel lymph node(s) near where the MCC arose. Treatment by radiation or surgery of the area where those involved node(s) were markedly lowers the risk of MCC recurring within that area.1
Who this works for
Patients that have a primary tumor and no abnormal lymph nodes that can be felt on physical exam. The patient needs to be able to undergo surgery (general anesthesia is usually required).
Who this doesn’t work for
If a patient does not want more accurate information as to whether the cancer has spread (perhaps because they would not want further treatment), then this procedure is not indicated. If a patient already has an abnormal/enlarged lymph node in the area near the tumor, then an ultrasound-guided biopsy biopsy The removal of cells or tissue in order to determine the presence, characteristics, or extent of a disease by a pathologist usually using microscopic analysis. of that abnormal node would normally be the appropriate next step to see if Merkel cell Merkel cell Merkel cells are found in the lower part of the epidermis. Although the exact function of Merkel cells is unknown, they are thought to be touch receptors. Also known as neuroendocrine cells, they have machinery similar to nerve cells and to hormone-secreting (endocrine) cells. carcinoma carcinoma Cancer that originates in the skin or in the tissues lining the gut and ducts. has spread to the node.
Often used in conjunction with
What to do next
If there is no spread of MCC to the nodes, typically no therapy is recommended for the area around the nodes. If MCC has spread to the sentinel lymph node, then either radiation therapy or surgery is recommended (but giving both does not improve chances of stopping the cancer from coming back in the nodes, and giving both surgery and radiation increases side effects such as lymphedema).2 Specifically, in several studies, it was found that in sentinel lymph node-positive patients that were managed with surgery and/or radiation therapy radiation therapy The use of radiation to kill cancer cells and shrink tumors. Merkel cell carcinoma is a highly radiation sensitive cancer in most cases. , there were no statistically significant differences in: disease control within the nodes, the length of time patients survive without having their cancer return, or overall survival.2 3 4 5
What is a lymph node?
The lymphatic system is a system of vessels and lymph nodes throughout the body. It serves an important function in the immune system. Lymph nodes act as filters to trap cancer cells as they travel through the lymphatic vessels. The lymph nodes that filter the legs are in the inguinal region between the thigh and the abdomen. The lymph nodes that filter the arms are in the armpit (axilla). Those that drain the skin of the face can be under the chin (submandibular), along the neck (cervical), or around the ears (pre/post-auricular).
What are the advantages of a sentinel lymph node biopsy?
Because MCC has already spread to the adjacent lymph nodes that feel normal in nearly one third of cases at diagnosis, figuring out whether this has happened or not helps in properly “staging” a patient, and thus in more accurately predicting the chance the cancer will recur. If the nodes are involved, treating them with radiation or surgery markedly reduces the risk the cancer will come back in those nodes.
- 1Gupta SG, Wang LC, Peñas PF, Gellenthin M, Lee SJ, Nghiem P. Sentinel lymph node biopsy for evaluation and treatment of patients with Merkel cell carcinoma: The Dana-Farber experience and meta-analysis of the literature. Arch Dermatol. 2006;142(6):685-690. doi:10.1001/archderm.142.6.685
- 2Fang LC, Lemos B, Douglas J, Iyer J, Nghiem P. Radiation monotherapy as regional treatment for lymph node-positive Merkel cell carcinoma. Cancer. 2010;116(7):1783-1790. doi:10.1002/cncr.24919
- 3Hruby, G., Guminski, A. & Thompson, J.F. Management of Regional Lymph Nodes in Patients with Merkel Cell Carcinoma Following a Positive Sentinel Node Biopsy: Less May be More, But is Either Enough?. Ann Surg Oncol 26, 315–317 (2019). https://doi.org/10.1245/s10434-018-7076-3
- 4Perez MC, Oliver DE, Weitman ES, et al. Management of Sentinel Lymph Node Metastasis in Merkel Cell Carcinoma: Completion Lymphadenectomy, Radiation, or Both?. Ann Surg Oncol. 2019;26(2):379-385. doi:10.1245/s10434-018-6810-1
- 5Lee JS, Durham AB, Bichakjian CK, et al. Completion Lymph Node Dissection or Radiation Therapy for Sentinel Node Metastasis in Merkel Cell Carcinoma. Ann Surg Oncol. 2019;26(2):386-394. doi:10.1245/s10434-018-7072-7
The following clinical publications and scientific research provide additional in-depth information about sentinel lymph node biopsies.