Comparison of intraparenchymal and intradermal injection for identification of the sentinel node in patients with breast cancer.

BACKGROUND: Sentinel lymph node (SLN) mapping with radioisotope and blue dye has been advocated for the staging of clinically negative axillae in patients with breast cancer. The optimal radiotracer injection technique is still being defined. This study compares the results of intraparenchymal and intradermal injection of technetium 99m (Tc 99m) sulfur colloid to establish an optimal method for SLN localization.
METHODS: Consecutive patients (n = 435) with clinically T0-2N0 breast cancer had SLN biopsy performed by a single surgeon. All patients but one received injections of both blue dye and Tc 99m sulfur colloid; one patient had injection of blue dye only and was excluded from analysis. Blue dye injections were intraparenchymal in all patients. The results of intraparenchymal (n = 107) and intradermal (n = 327) injections of radioisotope were compared for the following endpoints: 1) successful SLN identification, 2) false-negative rate, and 3) ratio of SLN/axillary background isotope counts.
RESULTS: Intradermal radioisotope injection was as effective as intraparenchymal radioisotope injection, identifying the SLN in 99.4% and 92.5% of cases, respectively. False-negative rates for both radioisotope injection techniques were < or = 5%. Ratios of SLN/axillary background isotope counts were higher with intradermal than with intraparenchymal injection (193/1 vs 41/1). Patient follow-up has revealed no axillary recurrence of tumor.
CONCLUSIONS: Intradermal radioisotope injection for SLN identification appears to be a highly accurate technique with acceptable false-negative and SLN identification rates. Compared with intraparenchymal isotope injection, the intradermal technique is associated with higher levels of isotope uptake by the SLN, facilitating SLN identification.