Lymphoscintigraphic and intraoperative detection of the sentinel lymph node in breast cancer patients: the nuclear medicine perspective

Abstract

The concept of sentinel lymph node biopsy in breast cancer surgery relates to the fact that the tumor drains in a logical way via the lymphatic system, from the first to upper levels. Therefore, (1) the first lymph node met (the sentinel node) will most likely be the first one affected by metastasis, and (2) a negative sentinel node makes it highly unlikely that other nodes are affected. Sentinel lymph node biopsy would represent a significant advantage as a mini-invasive procedure, considering that, after operation, about 70% of patients are found to be free from metastatic disease, yet axillary node dissection can lead to significant morbidity. Although the pattern of lymphatic drainage from a breast cancer can be very variable, the mammary gland and the overlying skin can be considered as a biologic unit in which lymphatics tend to follow the vasculature. Considering that tumor lymphatics are disorganized and relatively ineffective, subdermal, and peritumoral injection of small aliquots of radiotracer is preferred to intratumoral administration. (99m)Tc-labeled colloids with most of the particles in the 100-200 nm size range would be ideal for radioguided sentinel node biopsy in breast cancer. Lymphoscintigraphy is an essential part of radioguided sentinel lymph node biopsy, as images are used to direct the surgeon to the site of the node. The sentinel lymph node should have a significantly higher count than background. After removal of the sentinel node, the axilla must be re-examined to ensure all radioactive sites are identified and removed for analysis. The success rate of radioguidance in localizing the sentinel lymph node in breast cancer surgery is about 94-97% in Institutions where a high number of procedures are performed, approaching 99% when combined with the vital blue dye technique. At present, there is no definite evidence that a negative sentinel lymph node biopsy is invariably correlated with a negative axillary status, except perhaps for T(1a-b) breast cancers, with size < or =1 cm. Randomized clinical trials should elucidate the impact of avoiding axillary node dissection in patients with a negative sentinel lymph node on the long-term clinical outcome of patients.