Breast Cancer

PV QA 4 - Poster Viewing Q&A 4

TU_6_3377 - External Validation of IBTR! 2.0 Nomogram for Prediction of Ipsilateral Breast Tumor Recurrence

Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3

External Validation of IBTR! 2.0 Nomogram for Prediction of Ipsilateral Breast Tumor Recurrence
B. M. Lee1, J. Chang1, Y. U. Cho2, S. Park2, H. S. Park2, J. Y. Kim2, J. H. Sohn3, G. M. Kim3, J. S. Koo4, K. C. Keum1, C. O. Suh1, and Y. B. B. Kim1; 1Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea, Republic of (South), 2Departments of Surgery, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea, Republic of (South), 3Departments of Internal medicine, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea, Republic of (South), 4Departments of Pathology, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea, Republic of (South)

Purpose/Objective(s): IBTR! 2.0 nomogram is web-based nomogram that predicts ipsilateral breast tumor recurrence (IBTR). We aimed to validate the IBTR! 2.0 using an external data set.

Materials/Methods: The cohort consisted of 2206 patients, who received breast conserving surgery and radiation therapy from 1992 to 2012 at our insitution, where wide surgical excision is been routinely performed. Discrimination and calibration were used for assessing model performance. Patients with predicted 10-year IBTR risk based on a IBTR! 2.0 nomogram score of <3%, 3-5%, 5-10%, and >10% were assigned to Groups 1, 2, 3, and 4, respectively. We also plotted calibration values to observe the actual IBTR rate against the nomogram-derived 10-year IBTR probabilities.

Results: The median follow up period was 73 (6-277) months. The area under the receiver operating characteristic curve was 0.607, showing modest accordance between the estimated and observed recurrence rate. Calibration plot confirmed that the IBTR! 2.0 nomogram predicted the 10-year IBTR risk higher than the observed IBTR rates in all groups. High discrepancies between nomogram IBTR predictions and observed IBTR rates were observed in overall risk groups. Compared with the original development dataset, our patients had fewer high grade tumors, less margin positivity, and less lymphovascular invasion, and more use of modern systemic therapies.

Conclusion: IBTR! 2.0 nomogram seems to have moderate discriminative ability with a tendency to over-estimating risk rate. Continued efforts are needed to ensure external applicability of published nomograms by validating the program using an external patient population.

Author Disclosure: B. Lee: None. J. Chang: None. S. Park: None.

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