Abstract P5-06-08: Predicting distant recurrence of ER+ HER2- breast cancer after 5 years of endocrine therapy: The CTS5-tool validation in real life
Authors: Van Cauwenberge Josephine , Sestak Ivana , Punie Kevin , Wildiers Hans , Floris Giuseppe , Vergote Ignace , Berteloot Patrick , Van Gorp Toon , Smeets Ann , Van Nieuwenhuysen Els , Han Sileny , Nevelsteen Ines , Weltens Caroline , Janssen Hilde , Neven Patrick 
Published: March 2020

Abstract
Purpose: Extended adjuvant hormone therapy improves estrogen receptor (ER)-positive breast cancer outcome. The total duration of endocrine therapy is still a subject for debate. The CTS5 score, developed by Dowsett et al1., predicts late distant recurrence (LDR) between years 5 and 10 after diagnosis in ER-positive invasive breast cancers in postmenopausal women. This LDR risk might be used to select patients for extended endocrine therapy. The CTS5 score is calculated using age at the start of endocrine therapy, tumor size, grade, and lymph node status. The aim of this study is the validation of this tool in a series of women from the UZ Leuven.
Methods: This retrospective cohort study included 1125 postmenopausal women consecutively diagnosed with invasive estrogen receptor (ER) positive breast cancer who stopped endocrine therapy after 4.5 to 5.5 years. Tissue was tested for ER positivity and considered positive if &gt;1% of tumor nuclei were stained. HER2 status was defined according to ASCO guidelines. Statistical analysis was performed by Cox proportional hazards models which determined the prognostic performance of the CTS5 score for LDR.
Results: A total of 1125 patients were included in this analysis, of which 1097 had a known HER2 status and 1023 were negative. 62 of 1125 (5.5%) developed an LDR between years 5 and 10. The continuous CTS5 was a significant predictor for LDR (HR =2.69 (1.99-3.60), p&lt;0.001). The tool was not significant in the HER2 positive population (n=74), but numbers were small with only 5 LDR recorded (HR=0.92 (0.32-2.66), p=0.88). Further analysis was performed in a strictly HER2-negative cohort. In this cohort, 8 of the 401 patients (2.0%) with a CTS5 predicted low risk (&lt;5% LDR risk) developed LDR, in the intermediate risk group (5-10% LDR risk) 16 out of 336 (4.8%) and in the high risk group (≥10% LDR risk) 32 out of 286 (11.2%) developed LDR.
Conclusion: In our series of postmenopausal women, CTS5 accurately predicts late distant recurrence in ER-positive, HER2-negative early invasive breast cancers. The CTS5-score, identifying a patient group with LDR risk of ≥5%, might be used to discuss the benefits of extended endocrine therapy for individual patients. However, the exact predictive value for the benefit of prolonged therapy can only be based on a randomized controlled trial (RCT) using the LDR risk as a stratification factor.
It would be of great value to expand the study population, especially HER2-positive tumors, and define the prognostic performance of the CTS5 score in premenopausal women. Further research is needed.
1. Dowsett, M. et al. Integration of Clinical Variables for the Prediction of Late Distant Recurrence in Patients With Estrogen Receptor-Positive Breast Cancer Treated With 5 Years of Endocrine Therapy: CTS5. J. Clin. Oncol. 36, 1941-1948 (2018).
Citation Format: Josephine Van Cauwenberge, Ivana Sestak, Kevin Punie, Hans Wildiers, Giuseppe Floris, Ignace Vergote, Patrick Berteloot, Toon Van Gorp, Ann Smeets, Els Van Nieuwenhuysen, Sileny Han, Ines Nevelsteen, Caroline Weltens, Hilde Janssen, Patrick Neven. Predicting distant recurrence of ER+ HER2- breast cancer after 5 years of endocrine therapy: The CTS5-tool validation in real life [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-06-08.