Dermal injection of radioactive colloid is superior to peritumoral injection for breast cancer sentinel lymph node biopsy: Results of a multiinstitutional study

Objective To determine the optimal radioactive colloid injection technique for sentinel lymph node (SLN) biopsy for breast cancer. Summary Background Data The optimal radioactive colloid injection technique for breast cancer SLN biopsy has not yet been defined. Peritumoral injecti on of radioactive colloid has been used in most studies. Although dermal in jection of radioactive colloid has been proposed, no published data exist t o establish the false-negative rate associated with this technique. Methods The University of Louisville Breast Cancer Sentinel Lymph Node Stud y is a multiinstitutional study involving 229 surgeons. Patients with clini cal stage T1-2, NO breast cancer were eligible for the study. All patients underwent SLN biopsy, followed by level I/II axillary dissection. Peritumor al, subdermal, or dermal injection of radioactive colloid was performed at the discretion of the operating surgeon. Peritumoral injection of isosulfan blue dye was performed concomitantly in most patients. The SLN identificat ion rates and false-negative rates were compared. The ratios of the transcu taneous and ex vivo radioactive SLN count to the final background count wer e calculated as a measure of the relative degree of radioactivity of the no des. One-way analysis of variance and chi-square tests were used for statis tical analysis. Results A total of 2,206 patients were enrolled. Peritumoral, subdermal, or dermal injection of radioactive colloid was performed in 1,074, 297, and 5 11 patients, respectively. Most of the patients (94%) who underwent radioac tive colloid injection also received peritumoral blue dye injection. The SL N identification rate was improved by the use of dermal injection compared with subdermal or peritumoral injection of radioactive colloid. The false-n egative rates were 9.5%, 7.8%, and 6.5% (not significant) for peritumoral, subdermal, and dermal injection techniques, respectively. The relative degr ee of radioactivity of the SLN was five- to sevenfold higher with the derma l injection technique compared with peritumoral injection. Conclusions Dermal injection of radioactive colloid significantly improves the SLN identification rate compared with peritumoral or subdermal injectio n. The false-negative rate is also minimized by the use of dermal injection . Dermal injection also is associated with SLNs that are five- to sevenfold more radioactive than with peritumoral injection, which simplifies SLN loc alization and may shorten the learning curve.