Background: Radioisotope mapping is an essential technical component of sentinel lymph node (SLN) biopsy, and most authors define isotope success by an arbitrary threshold SLN-to-background ratio. Few studies have examined the degree to which the relative level of SLN counts correlates with the presence of metastasis. Having removed the SLN with the highest counts, how far should the surgeon persist in removing additional SLN which contain much lower levels of isotope?
Methods: We performed SLN biopsy, using both radioisotope and blue dye, in 2285 consecutive patients with stage I-II breast cancer. Successful isotope localization was defined as an ex vivo SLN-to-axillary background count ratio of at least 4:1, and enhanced pathologic analysis (serial sections and immunohistochemistry) was used throughout.
Results: Among the 1566 patients with more than one SLN site identified, the SLN contained metastasis in 463 (30%). In 369 (80%) of these SLN-positive cases, the SLN with the highest count contained tumor, but in 94 (20%) it was benign. Among these 94: (1) the counts of the hottest benign SLN exceeded those of the histologically positive SLN by a ratio of at least 10:1 in 31% (29 of 94) of cases, (2) the counts of the positive SLN were < 4:1 those of the axillary background in 16% (15 of 94) of cases, and (3) blue dye failed to identify 27% of positive SLN. No optimum ratio of SLN-to-SLN or SLN-to-background counts identified the positive SLN in all cases.
Conclusion: Although the SLN with the highest counts is positive in 80% of breast cancer patients with multiple SLN, neither a relatively high isotope count nor the presence of blue dye consistently predict SLN positivity in all breast cancer patients. For maximum accuracy, SLN biopsy requires (1) the removal of all nodes containing isotope regardless of the relative magnitude of counts, (2) the concurrent use of blue dye to salvage those procedures in which isotope fails, and (3) the removal of all clinically suspicious non-SLN.