Use and limitations of a nomogram predicting the likelihood of non-sentinel node involvement after a positive sentinel node biopsy in breast cancer patients.

After a positive sentinel lymph node (SLN) biopsy, some patients may be considered to have a very low risk of non-SLN involvement and could be candidates for axillary sparing. The aim of this study was to validate the nomogram created at the Memorial Sloan-Kettering Cancer Center (MSKCC) for the prediction of non-SLN involvement in an independent set of 140 patients with both positive SLNs and axillary dissection. The predicted proportions of positive non-SLNs were compared with the observed percentages of non-SLN metastasis. Although the SLN metastasis size and tumor size did influence the risk of non-SLN involvement, the correlation between the predicted and observed proportions was weaker for our patients (R: 0.84) than for the patients assessed at the MSKCC (R: 0.97). Differences were noted in the intraoperative assessment and in the final histology of the SLNs (imprints vs frozen sections and more detailed vs less detailed, respectively), and these could partly explain the lower level of the correlation. The nomogram could not be validated and was found to be of only limited use for the prediction of non-SLN involvement in patients operated on under similar, though not fully identical conditions. We therefore warn against the unvalidated use of this prediction tool.