Numerous studies have shown that sentinel lymph node biopsy (SLN) has a high level of detection sensitivity. Successful detection procedure depends on the amount of radioactivity and accumulation of blue dye in the SN. Our aim was to relate the differences observed in intraoperative SN presentation to tumor burden, characteristics of the primary tumor and patient attributes. Our retrospective analysis included 369 patients undergoing SLN in the Department of Gynecology of the University Hospital of Zurich within five years. Data was collected from the patients (age, BMI), the primary tumor (size, grading, hormone receptors, HER2 status) and the SNs removed (counts per second [cps], blue dye, size of nodular metastasis, extracapsular involvement, number of SNs excised). Because patients typically had more than one SN, a linear mixed-effects model was used to account for the clustering within one patient. SNs presented with significantly lower radioactivity in elderly (-1.8%/year, p < 0.001) and obese patients (-3.9%/kg/m2, p = 0.006) as well as in G3 primary tumors (p = 0.002). Radiocolloid accumulation decreased with increasing metastasis size (-6.1%/mm, p = 0.006). In conclusion the detection procedure of SNs is mainly affected by the patient's age and BMI and by nodular metastasis' size. Phagocytotic activity in the lymph node may increase radiotracer accumulation, showing the highest tracer signals in micrometastatic SNs. In large SN metastasis the lymph flow appears obstructed, reducing the axillary drainage and therefore making detection procedure difficult.
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