Sentinel lymph node mapping in breast cancer and melanoma

Sentinel lymph node biopsy replaced routine full axillary or regional lymph node dissection for clinically node-negative breast cancer and melanoma, because the sentinel node - the first node draining the tumour site - accurately predicts the status of the rest of the nodal basin, and removing it alone causes far less lymphoedema and morbidity. Lymphoscintigraphy maps that node before surgery: a radiocolloid (Tc-99m sulfur colloid, albumin colloid, or antimony trisulphide colloid depending on jurisdiction) or the receptor-targeted agent Tc-99m tilmanocept is injected around the tumour or biopsy site, and a gamma camera images its lymphatic drainage over the following one to twenty-four hours.

The joint EANM/SNMMI practice guidelines for breast cancer and for melanoma specify injection technique (peritumoral, subdermal, periareolar or intradermal depending on the setting), imaging timing (early dynamic imaging immediately after injection to see the draining lymphatic channel, then delayed static images at 1-4 hours and sometimes up to 18-24 hours), and processing including SPECT/CT for anatomically complex drainage such as head and neck melanoma or extra-axillary breast drainage. Tc-99m tilmanocept, approved by the FDA in 2013, targets the mannose-binding CD206 receptor on macrophages within lymph nodes rather than relying on particle size for retention, giving more reliable single-node localisation with less second-echelon node uptake than traditional colloids.

In the operating theatre, a handheld gamma probe locates the radioactive node(s) intraoperatively, often combined with blue dye or, increasingly, a fluorescent tracer, for direct visual confirmation; the dual technique (radiotracer plus dye) achieves the highest sentinel node identification rates. The procedure has a low radiation burden to both patient and staff and no significant contraindications beyond pregnancy precautions and rare tracer hypersensitivity.