Gamma probe-guided sentinel node biopsy—optimal timing for injection

Aims. We initiated a Phase I feasibility study using a gamma-detecting probe (GDP) and radiolabelled colloid to localize the sentinel lymph node (SLN) in breast cancer. The aim of the study was to establish the ideal timing for injection and examine any possible exclusion criteria for this method. Methods. Thirty breast cancer patients diagnosed by fine needle aspiration (FNA) were included in this study. All were injected with 60 M Bq rhenium colloid labelled with 99mTc (Tck-17). Scintigraphy was done 20 min, 2, 6 and 25 hours post-injection. Patients were then taken to surgery where they were injected with patent blue dye. During surgery, the SLN was located with a GDP (Neoprobe® Model 1000). In 28 patients, the SLN was identified by scintigraphy 2 hours after injection, identical to the images seen after 24 hours. Results. In all 28 patients, the SLN was found by the GDP during surgery. In 26 patients the SLN was dyed blue. The two patients with no SLN localization had received prior radiation. Pathology disclosed SLNs with metastases in seven patients. Two patients had a negative SLN but had an axillary lymph node replaced by tumour. Conclusions. Two to 24 hours prior to surgery is suitable timing for injection. Previous radiotherapy predicts failure for this procedure. Further studies are needed to find the exact false-negative rate of this method for breast cancer.