Sentinel Lymph Node Biopsy — Lymph Node Staging Procedure

The lymphatic system acts as a primary route for cancer cells departing a solid tumour. The sentinel node is defined as the initial lymph node, or cluster of nodes, that receives direct lymphatic drainage from the primary tumour site. If cancer cells have migrated, they are statistically most likely to appear in these specific sentinel nodes before travelling further.

During an SLNB, a surgeon injects a radioactive tracer, a blue dye, or a magnetic nanoparticle near the tumour. Specialised detection devices track the substance to isolate the sentinel nodes, which are surgically excised and submitted for pathological review. If clear, remaining regional nodes are preserved.

Historically, evaluating lymphatic spread required clearing large groups of regional lymph nodes, leading to frequent complications such as chronic lymphedema, chronic pain, and limited joint mobility. An SLNB reliably identifies micro-metastases while minimising surgical trauma.

Knowing whether the sentinel node contains cancer cells is essential for accurate staging. The result dictates whether a patient needs additional therapies, such as adjuvant chemotherapy, radiotherapy, or targeted immunotherapy, directly shaping the overall management roadmap.

SLNB relies on technetium-99m radiotracers, indocyanine green (ICG) fluorescence, or isosulfan blue dye injected pre-operatively. Intraoperative gamma probes or near-infrared cameras identify hot or fluorescent nodes. Pathologists then perform serial sectioning, haematoxylin and eosin (H&E) staining, and cytokeratin immunohistochemistry to identify isolated tumour cells or macrometastases.

Sentinel lymph node biopsy is standard practice primarily in early-stage breast cancer and cutaneous melanoma. It is also increasingly utilised in select cases of gynaecological malignancies, such as endometrial and cervical cancers, as well as specific head and neck cancers and penile carcinomas, helping avoid full lymphadenectomies.

A negative sentinel node biopsy generally eliminates the need for further axillary or regional nodal dissection, protecting against severe lymphedema. A positive result indicates regional disease and guides choices regarding subsequent axillary radiotherapy, targeted therapy, or adjuvant systemic treatments to eradicate residual micro-metastatic cancer.