Intradermal isotope injection is superior to intramammary in sentinel node biopsy for breast cancer

Background. The optimal sentinel lymph node (SLN) biopsy technique remains undefined in breast cancer Injecting radiotracer or blue dye by a variety of routes seems to stage the axilla with comparable accuracy, and we have hypothesized that the dermal and the parenchymal lymphatics of the breast drain to the same SLN in most patients. Two previous studies from our institution support this concept: (1) a single-surgeon series of 200 consecutive SLN biopsy procedures demonstrating a high dye-isotope concordance for both intradermal (ID) and intraparenchymal (IP) isotope injection, and (2) a series of 100 procedures validated by a backup axillary dissection (ALND) in which the false-negative rate following ID isotope injection was comparable to that of our previous results with IP injection. Here, we directly compare the results of SLN biopsy using either ID or IP isotope injection for our entire experience of SLN biopsy procedures in which a backup ALND was done. Methods. This is a retrospective, nonrandomized study of 298 clinical stage I to II breast cancer patients having SLN biopsy with a backup ALND planned in advance, comparing the results of ID (n = 164) and IP (n = 134) isotope injection. All patients had IP injection of blue dye. Endpoints included (1) successful SLN identification, (2) false-negative rate, (3) dye-isotope concordance, and (4) the SLN/axillary background isotope count ratio. Results. ID isotope was more successful than IP, identifying the SLN in 98 % versus 89 % of cases, respectively. False-negative results (4.8 % vs 4.4 %) and dye-isotope concordance (92 % vs 93 %) were comparable between the 2 groups, and SLN/axillary background isotope count ratios were significantly higher with ID than with IP injection (288/1 vs 59/1). Conclusions. ID isotope injection identifies the SLN more often than IP, stages the axilla with comparable accuracy, and is associated with higher Levels of SLN isotope uptake. The dermal and parenchymal lymphatics of the breast drain to the same axillary SLN in most breast cancer patients, and ID isotope injection is the procedure of choice in this setting.