Multicenter validation of two nomograms to predict non-sentinel node involvement in breast cancer

Nomograms are used to predict the involvement of non-sentinel nodes (nSN) in breast cancer. This study attempts to externally validate two of the more commonly used nomograms (MSKCC and Stanford University). Five hundred and one cases of positive SNB with posterior axillary lymphadenectomy from 11 Spanish hospitals with widespread experience of the technique were studied. In all cases, an estimate of the probability of nSN involvement was made using the MSKCC and the Stanford University nomograms. Discrimination was assessed by calculating the area under the receiver operating characteristic curve. To assess the calibration of the nomogram, observed probability was plotted against the nomogram-calculated predicted probability. The overall predictive accuracy of the MSKCC nomogram was 0.684 (95 % confidence interval, 0.635-0.732), while in the case of that from Stanford the predictive accuracy was 0.658 (95 % confidence interval 0.607-0.709). The mean predicted probability of nSN metastases in each group of patients was correlated with the observed probability with an acceptable concordance (r = 0.820; p < 0.004 in MSKCC nomogram and r = 0.888; p < 0.001 in Stanford nomogram). These nomograms can be useful tools in the evaluation of patients with breast cancer and positive sentinel nodes but other factors, including a comprehensive clinical assessment, must be used to decide the most appropriate surgical approach for an individual patient, especially with regard to avoiding unnecessary lymphadenectomy.