Prediction of involvement of sentinel and nonsentinel lymph nodes in a Canadian population with breast cancer.

BACKGROUND We sought to identify criteria for the intraoperative assessment of sentinel lymph node (SLN) involvement in women with early breast cancer. We also sought to determine whether the SLN nomogram developed by the Memorial Sloan-Kettering Cancer Center (MSKCC) to predict nonsentinel lymph node (NSLN) involvement when the SLN is positive would accurately predict NSLN involvement in our patient population. METHODS We performed 405 SLN biopsies in 397 women between January 1998 and June 2005. We determined factors associated with SLN metastases using univariate and multivariate logistic regression. Ninety women who had 1 positive SLN or more and underwent axillary lymph node dissection (ALND) had complete data for analysis. We applied the MSKCC nomogram retrospectively to this subset of women, and we calculated the probability of NSLN involvement and compared it with the observed rate. RESULTS Multifocality and the presence of lymphovascular invasion were predictive of SLN involvement. Ductal carcinoma in situ was negatively associated with SLN involvement. Intraoperative evaluation identified 57 (63%) of the 90 women with involved SLN, of which 26 (29%) had involved NSLN. Application of the MSKCC nomogram to our data set produced an area under the receiver operator characteristic curve of 0.71. The nomogram tended to overestimate the probability of NSLN involvement in our population. CONCLUSION Lymphovascular invasion and multifocality were associated with SLN involvement. Women with small low-grade tumours may not require routine intraoperative evaluation of SLNs. The MSKCC nomogram appears to be most useful as a decision aid in selecting those women with an involved SLN in whom ALND may be omitted.