Influence of the new AJCC breast cancer staging system on sentinel lymph node positivity and false-negative rates

The sixth and newest edition of the American Joint Committee on Cancer (AJCC) staging system for breast cancer now defines axillary sentinel lymph nodes with micrometastatic deposits 0.2 mm in diameter or smaller as node-negative. The aim of this study was to determine how this new classification scheme would affect axillary sentinel lymph node positivity, false-negative rate, and overall accuracy of an inception cohort of 205 breast cancer patients undergoing definitive surgery that included sentinel lymph node biopsy plus level I/II axillary lymphadenectomy. Based on the previous AJCC system for staging breast cancer, in which all sentinel lymph node metastases were considered positive, the rate of nodal positivity in this cohort was 47%, the overall accuracy was 99%, and the false-negative rate was 2.1%. According to the new classification system, the rate of nodal positivity in this cohort was 39.5% and the overall accuracy was 98%. The false-negative rate rose to 4.9% because two patients with micrometastatic deposits 0.2 mm or smaller, which are considered node-negative in the new system, had macroscopically positive disease in non-sentinel lymph nodes found in the completion lymphadenectomy.