Validation of the web-based IBTR! 2.0 nomogram to predict for ipsilateral breast tumor recurrence after breast conserving therapy

Publication date: Available online 2 April 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Isabelle Kindts, Annouschka Laenen, Stephanie Peeters, Hilde Janssen, Tom Depuydt, Ines Nevelsteen, Erik Van Limbergen, Caroline Weltens
PurposeA nomogram to predict the 10-year ipsilateral breast tumor recurrence (IBTR) after breast conserving therapy (BCT) with and without radiotherapy for breast cancer (BC) was developed based on seven literature-derived clinicopathologic variables with a concordance index (C-index) of 0.66 on independent validation. The aim of this study was to evaluate this IBTR! 2.0 model.Methods and MaterialsWe retrospectively identified 1898 BC cases, treated with BCT and radiotherapy at the XXX from 2000 to 2007 with requisite data for the nomogram variables. Clinicopathologic factors were assessed. Two definitions of IBTR were considered where simultaneous regional or distant recurrence were either censored (conform IBTR! 2.0) or included as event.Validity of the prediction algorithm was tested in terms of discrimination and calibration. Discrimination was assessed by the concordance probability estimate (CPE) and Harrell's C-index. The mean predicted and observed 10-year estimates were compared for the entire cohort and for four risk groups predefined by nomogram-predicted IBTR risks and a calibration plot was drawn.ResultsMedian follow-up was 10.9 years. The 10-year IBTR rates were 1.3 % and 2.1 %, according to the two definitions of IBTR.The validation cohort differed from the development cohort with respect to the administration of hormonal therapy, surgical section margins, lymphovascular invasion and tumor size. In univariable analysis, a younger age (p = 0.002) and a positive nodal status (p = 0.048) were significantly associated with IBTR with a trend for the omission of hormonal therapy (p = 0.061).The CPE and C-index varied between 0.57 to 0.67 for the two definitions of IBTR. In all four risk groups, the model overestimated the IBTR risk. In particular between the lowest-risk groups a limited differentiation was suggested by the calibration plot.ConclusionsThe IBTR! 2.0 predictive model for IBTR in BC patients shows substandard discriminative ability with an overestimation of the risk in all subgroups.

Teaser

Local failures after breast conserving therapy correlate with overall survival. Accurate prediction of these failures might alter therapeutic strategies. The IBTR! 2.0 nomogram predicts the 10-year ipsilateral breast tumor recurrence and has been made available in an online application. Our findings have validated the algorithm and conclude that it shows substandard discriminative ability with an overestimation of the risk in all subgroups.


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