This page is general information, not medical advice. Your own doctor or care team is the right source for questions about your skin, diagnosis or treatment.
A sentinel lymph node biopsy is a staging procedure used after cancer has been diagnosed. It examines tissue from a lymph node rather than the original skin spot. The word sentinel describes the node's position in a drainage pathway; it does not mean that the node is known to contain cancer.
A discussion about this procedure can involve the purpose of the test, what different results would mean and the possible harms. Those questions belong to the clinical situation. This page explains the procedure and the research vocabulary without suggesting that anyone have or decline it.
Lymph drainage and the sentinel node
The National Cancer Institute's sentinel-node fact sheet describes lymph nodes as small organs in the lymphatic system. This system is part of the immune system. Its vessels carry lymph, a clear fluid containing white blood cells and material from body tissues. Nodes filter that fluid.
In a person with cancer, lymph may also carry cancer cells from the primary tumor, meaning the original tumor. A sentinel lymph node is the node to which cells from that tumor are most likely to spread first. The NCI notes that more than a single node may have this role.
The drainage pathway is why the procedure uses mapping. A simple diagram can show fluid traveling from a skin area toward a node. It describes a general pathway, not a map of the nodes in any reader's body. The location and pattern are assessed during the clinical procedure.
How mapping and examination are described
The NCI describes a surgeon placing a radioactive tracer, a blue dye, or both near the tumor. These materials travel with lymph. The surgeon identifies nodes containing the tracer or dye, makes an incision and removes the identified sentinel node tissue.
A pathologist, a doctor trained to identify disease in tissue, examines the removed node for cancer cells. The NCI explains that the procedure is often performed with removal of the primary tumor, although the sequence may differ. It may be outpatient care or involve a hospital stay. Those arrangements are specific to the planned procedure.
Mapping, removing tissue and examining tissue are separate parts of the process. Mapping identifies which node receives drainage. The laboratory examination looks for cancer in that node. A diagram or a physical examination cannot supply the microscopic result.
The result is recorded as part of the tissue findings. The explanation of melanoma pathology reports covers how node information may appear alongside findings from the skin sample. Your care team can explain which specimens were examined and how the reports relate.
What the result contributes to staging
A negative result means cancer cells were not identified in the examined sentinel node. A positive result means they were found. The NCI says this information helps establish the extent of the cancer and informs treatment planning. A positive result does not, by itself, establish that cancer is present in a distant organ.
The American Cancer Society's staging explanation combines findings about the skin tumor, nearby nodes and distant spread. When melanoma is identified in nearby nodes without distant spread, the finding contributes to a stage III description. The page on stage III melanoma explains that outline and the categories agencies discuss.
The NCI also describes false-negative results: cancer cells are not seen in the sampled node even though spread has occurred. This is a limitation of the procedure. A negative result is part of an assessment, rather than a guarantee about every tissue or organ. The treating team considers it with the other available findings.
Possible harms
The NCI lists pain, bruising, swelling, numbness or tingling, infection risk and difficulty moving the affected area among possible effects of node surgery. A reaction to the mapping dye is also possible. These are possible harms, not a list of effects that every person will experience.
Removal of lymph nodes can disrupt fluid drainage. A buildup of lymph fluid can cause swelling called lymphedema. A collection of fluid near the surgical site is called a seroma. The NCI describes fewer side effects with removal of fewer nodes, while making clear that sentinel node biopsy still carries risks.
These general descriptions do not provide care instructions for symptoms after surgery. The clinical team can explain the risks of the planned procedure, the follow-up arrangements and how they assess postoperative changes.
What the trials examined
A randomized trial reported in the New England Journal of Medicine compared wide removal of the skin melanoma with node observation against skin surgery with sentinel-node biopsy and further node removal when the biopsy found melanoma. In the overall study population, the report found no statistically significant difference in melanoma-specific survival between the treatment groups. It reported better disease-free survival in the biopsy group for intermediate-thickness and thick melanomas.
Disease-free survival concerns time without recurrence or spread. Melanoma-specific survival concerns deaths from melanoma. Those are different study outcomes. The findings concerned the participants and the trial's approach to care; they do not predict a reader's outcome or settle whether a procedure applies to that person.
A separate randomized trial in the same journal studied people whose sentinel nodes contained melanoma. It compared immediate completion lymph node dissection, removal of the remaining regional nodes, with node observation that included ultrasound. Immediate dissection improved control of disease in the regional nodes but did not increase melanoma-specific survival in the analyzed study population. Lymphedema was more frequent in the dissection group, and the report cautioned about interpreting some secondary findings.
This was a comparison after a positive sentinel-node result, rather than a comparison of whether to perform the initial biopsy. Observation in that trial meant a defined clinical monitoring approach. It did not mean leaving care aside. The findings are context for a discussion with the care team, whose explanation includes the actual node findings and other relevant information.