Credentialing for breast lymphatic mapping: how many cases are enough?

OBJECTIVE: To evaluate credentialing issues for sentinel lymphatic mapping for breast cancer. SUMMARY BACKGROUND DATA: The sentinel lymph node (SLN) is defined as the first lymph node receiving lymphatic drainage from a tumor. The SLN accurately reflects the status of the axillary nodes in patients with early-stage breast cancer, and SLN mapping is gaining widespread acceptance. Few of the many published feasibility studies of lymphatic mapping for breast cancer have adequate numbers to assess credentialing issues for this new procedure.
METHODS: Five hundred consecutive SLN biopsies were performed at one institution, over a 20-month period, by eight surgeons, using isosulfan blue dye and technetium-labeled sulfur colloid. The authors reviewed each surgeon's success rate in finding the SLN, and false-negative rate, relative to level of experience with the technique.
RESULTS: Lymphatic mapping performed by an experienced surgeon (surgeon A, B, or C) was associated with a higher success rate (94%) than when it was performed by one with less experience (86%). Ten failed mapping procedures occurred in the first 100 cases. For each of the ensuing 100 cases, there were eight, six, six, and four failed mapping procedures, suggesting that increasing experience does not eradicate failed mapping procedures completely. The false-negative rate among 104 patients in whom axillary dissection was planned in advance was 10.6% (5/47). Most false-negative results occurred early in the surgeon's experience: when the first six cases of every surgeon were excluded, the false-negative rate fell to 5.2% (2/38).
CONCLUSIONS: With increasing experience, failed SLN localizations and false-negative SLN biopsies occur less often. Combined dye and isotope localization, enhanced histopathology, a backup axillary dissection, and judicious case selection are required to avoid the high false-negative rate of one's early experience.