The sentinel node biopsy (SNB) is a common surgical procedure that determines if cancer cells have spread from a primary tumor to the nearest lymph nodes. This technique identifies and removes the “sentinel” lymph node—the first node to receive drainage from the tumor site—for analysis. A positive SNB means cancer cells have traveled through the lymphatic system, significantly altering the patient’s staging and treatment plan. This finding shifts the focus from local treatment to a comprehensive strategy for managing a more widespread disease.
Interpreting the Positive Result
A positive sentinel node biopsy indicates cancer cells have left the primary tumor and lodged in the first regional lymph filter. The influence of this finding depends heavily on the volume of cancer cells detected, which pathologists categorize by measuring the size of the clusters.
The smallest finding is isolated tumor cells (ITCs), deposits measuring 0.2 millimeters or less, or fewer than 200 individual cells. Next are micrometastases, which are clusters ranging from greater than 0.2 mm up to 2 mm in size. The largest finding, macrometastases, involves cancer deposits larger than 2 mm within the sentinel node.
This size distinction correlates with the likelihood of finding cancer in other lymph nodes and dictates subsequent treatment intensity. Micrometastases or ITCs are often considered low-volume disease, potentially allowing for less aggressive surgery. Conversely, macrometastases represent a higher disease burden and generally necessitate a more extensive surgical or non-surgical approach to the remaining lymph nodes.
Further Evaluation for Disease Staging
A positive sentinel node biopsy confirms the cancer has begun to spread and is a risk factor for distant metastasis. This result prompts a comprehensive evaluation, known as complete staging, to ensure the cancer has not reached distant organs like the bones, lungs, or liver. Determining the overall extent of the disease is essential.
Multidisciplinary teams often recommend routine, full-body imaging, particularly for cases with macrometastases or other high-risk features. Common imaging tests include a computed tomography (CT) scan of the chest, abdomen, and pelvis, and a bone scan. Some centers also use a positron emission tomography (PET) scan, often combined with a CT scan (PET/CT), which can be sensitive in detecting small metastases.
The goal of these studies is to detect unsuspected spread that would change the cancer’s stage to Stage IV. Finding distant disease fundamentally shifts the treatment goal from curative to palliative. This alters the treatment plan, often prioritizing systemic therapy over local surgical intervention.
Treatment Decisions and Subsequent Surgery
The most immediate consequence of a positive sentinel node result is the decision regarding further surgical intervention in the lymph node basin. Historically, a positive finding mandated a complete Axillary Lymph Node Dissection (ALND), which involves removing most or all remaining lymph nodes in the area. Modern clinical trials have significantly changed this approach, especially for patients with breast cancer and melanoma.
Current practice often avoids routine ALND for patients with limited disease, such as those with one or two positive sentinel nodes undergoing breast-conserving surgery followed by radiation. Studies demonstrated that omitting ALND in these select, low-risk patients did not reduce survival rates. This de-escalation reduces the risk of long-term complications like lymphedema, a chronic arm swelling.
The volume of disease found in the sentinel node is the primary factor guiding this decision. Patients with micrometastases may be spared further surgery, with radiation therapy to the lymph node basin used instead. Patients with macrometastases or multiple positive sentinel nodes are more likely to require an ALND for better regional disease control. The final decision is personalized based on the tumor’s characteristics, the patient’s overall health, and the planned local treatment.
Planning Adjuvant and Systemic Therapies
A positive lymph node status is a strong indicator that a patient will benefit from adjuvant therapy, which is treatment given after surgery to eliminate remaining cancer cells. The finding confirms the cancer has entered the bloodstream or lymphatic system, increasing the risk of recurrence elsewhere. The positive SNB result is a powerful factor in determining the necessary combination of systemic and regional treatments.
Radiation therapy to the lymph node area, known as regional nodal irradiation, is often recommended to target any microscopic disease left behind. This local treatment improves disease control and is used as an alternative or addition to ALND.
Systemic treatments are intensified based on the positive nodal status. These may include chemotherapy, hormone therapy for sensitive tumors, or targeted therapies that block specific growth pathways. For example, a positive node in high-risk breast cancers after neoadjuvant chemotherapy may prompt the use of specific drugs to improve outcomes.