Learning curves and breast cancer lymphatic mapping: institutional volume index

Introduction. To date, studies of breast cancer lymphatic mapping (LM) have analyzed success with respect to individual surgeons. However, LM and sentinel lymph node biopsy (SLNBx) are procedures that require institutional multidisciplinary cooperation between the departments of radiology, pathology, and surgery. Thus, it is important to evaluate these procedures with respect to the institution. This study examines 30 institutions to clarify the value of the institutional volume index (IVI) (cases/month) to the outcome of LM and SLNBx in breast cancer. Methods. From July 1997 to July 1999, 30 institutions participated in the Department of Defense national breast LM trial. All participants underwent a 2-day training course for surgeons, nuclear medicine physicians, and pathologists. The records for each institution were prospectively accrued and submitted to a database. The false negatives, failure rates, and IVI were calculated for each institution. A logistic regression model plots the relationship between IVI and institutional failure rate. Using a multivariate analysis, mapping failure was analyzed as a function of case number with respect to the individual surgeon and the institution as a whole. Results. False negative results were demonstrated in only 5 (4%) cases among all institutions and were excluded from further analysis due to small numbers. Mapping failures were found in all but 7 of the 30 institutions whose data were complete. There were 71 mapping failures among 74 surgeons over 555 cases, which yielded an overall failure rate of 12.79% (71 555). The logistic regression model revealed an inverse relationship between IVI and institutional failure rate. However, the multivariate analysis revealed that the individual surgeon performance was the most significant factor in determining institutional mapping success. Conclusion. Failure to map can be a function of multiple factors including surgical skill, surgical volume index, and injection method of the SLN patient, all under the quality control of an institution. The surgical failure rate on the other hand is a function of surgical skill, surgical volume, and injection methods. While differences in mapping success exist across institutions, this disparity is not due to factors associated with the institution as a whole, but lie with the individual surgeon.