Validation of a breast cancer nomogram for predicting nonsentinel lymph node metastases after a positive sentinel node biopsy

Background: Although completion lymph node dissection (CLND) is the standard of care for breast cancer patients with sentinel lymph node (SLN) metastases, the SLN is the only node with tumor in 40% to 60% of cases. To assist with decision-making regarding CLND, investigators at Memorial Sloan-Kettering Cancer Center devised and validated a nomogram for predicting the likelihood of non-SLN metastases. To assess the generalizable use of this nomogram, validation analysis was performed by using an external database. Methods: Eight clinicopathologic variables for 200 consecutive breast cancer patients at the University of Texas M. D. Anderson Cancer Center with SLN metastases and CLND were entered into the nomogram. The accuracy of the nomogram to predict non-SLN metastases was assessed by the receiver operating characteristic (ROC) curve and linear regression analysis. The accuracy of the nomogram with touch-imprint cytology (TIC) as a substitute variable for frozen section was also evaluated. Results: The linear correlation coefficient of the nomogram-predicted probabilities correlated with the observed incidence of non-SLN metastases for all patients (.97). The accuracy of the nomogram as measured by the area under the ROC curve was .71. When applied solely to patients who had TIC assessment of the SLN, the area under the ROC curve was .74. Conclusions: This study validated the Memorial Sloan-Kettering Cancer Center breast cancer nomogram by using an external database. TIC seems to be an acceptable substitute for frozen section as a nomogram variable. The nomogram may help predict an individual's risk of non-SLN metastases and assist in patient decision making regarding the benefit of CLND.