Validation over time of a nomogram including HER2 status to predict the sentinel node positivity in early breast carcinoma

BackgroundThe molecular subtypes of breast cancer have different axillary status. A nomogram including the interaction covariate between estrogen receptor (ER) and HER2 has been recently published (Reyal et al. PLOS One, May 2011) and allows to identify the patients with a high risk of positive sentinel lymph node (SLN). The purpose of our study was to validate this model on an independent population.MethodsWe studied 755 consecutive patients treated at Institut Curie for operable breast cancer with sentinel node biopsies in 2009. The multivariate model, including age, tumor size, lymphovascular invasion and interaction covariate between ER and HER2 status, was used to calculate the theoretical risk of positive sentinel lymph node (SLN) for all patients. The performance of the model on our population was then evaluated in terms of discrimination (area under the curve AUC) and of calibration (Hosmer–Lemeshow HL test).Resultsour population was significantly different from the training population for the following variables: median tumor size in mm, lymphovascular invasion, positive ER and age. The nomogram showed similar results in our population than in the training population in terms of discrimination (AUC = 0.72 [0.68–0.76] versus 0.73 [0.7–0.75] and calibration (HL p = 0.4 versus p = 0.35).ConclusionsDespite significant differences between the two populations concerning variables which are part of the nomogram, the model was validated in our population. This nomogram is robust over time to predict the likelihood of positive SLN according to molecular subtypes defined by surrogate markers ER and HER2 determined by immunohistochemistry in clinical practice.