Abstract P1-02-04: Real world adjuvant endocrine treatment in premenopausal breast cancer patients compared with the proposed algorithm using the Regan Composite Risk Score

Abstract Background The Regan Composite Risk Score (RCRS) is a web-based prognostic and predictive calculator to guide the use of adjuvant exemestane plus ovarian function suppression (AI + OFS) versus tamoxifen plus ovarian function suppression (TAM + OFS) or tamoxifen alone (TAM) for premenopausal women with hormone receptor-positive HER2-negative early breast cancer (HR+/HER2- EBC). We compared our adjuvant endocrine therapy policy based on the tumor board with the treatment guided by the RCRS during 2 time periods, one before and one after the acquaintance of the Tamoxifen and Exemestane Trial (TEXT) and Suppression and Ovarian Function Trial (SOFT) data. This allowed us to see a possible evolution in therapy policy. Methods A retrospective cohort study of 563 premenopausal patients with HR+/HER2- and HER2+ EBC diagnosed at the University Hospital of Leuven during 2 periods, 2010-2012 (cohort 1) and 2015-2017 (cohort 2), was conducted. For each patient with HER2- EBC, the RCRS was calculated by entering the requested characteristics in the online available tool. The primary outcome was to investigate how frequent our therapy differed from the therapy guided by the RCRS based on the estimated 8-yr distant relapse free interval (DRFI) with an arbitrary cut-off set at 3 %. If the received therapy was ≥ 3 % less efficient in 8-year DRFI compared to the optimal therapy according to RCRS, the patient was considered undertreated. If the received therapy differed by less than 3 % in 8-year DRFI compared to the optimal therapy according to RCRS and yet the most intensive therapy (AI + OFS > TAM + OFS > TAM) was administered, the patient was considered overtreated. In the other cases, the patient was considered to have been treated concordant with the RCRS. Secondarily, nonadherence of the HER2- and HER2+ patients towards the endocrine treatments leading to therapy switch because of intolerance was recorded at 6, 12, 24 and 36 months. Analyses were performed using SAS software and the comparison of both cohorts was performed by the chi-squared test for categorical variables. Results According to the RCRS, 43.2 % (89/206) of the HER2-negative patients of cohort 1 were undertreated compared to 22.1 % (43/194) in cohort 2 (chi- squared test, p-value < 0.001). The number of overtreated patients also differed significantly between the two cohorts (chi-squared test, p-value = 0.003) with 2.9 % (6/206) in the first cohort and 10.3 % (20/194) in the second cohort. Finally, the number of patients treated concordant with the guidance derived from the RCRS was 53.9 % (111/206) in cohort 1 and 67.5 % (131/194) in cohort 2 (chi-squared test, p-value = 0.005). Treatment intolerance and switch was observed in 34.8 %, 16.7 % and 12.4 % of the patients receiving AI + OFS, TAM + OFS or TAM as initial therapy respectively; this was numerically higher for all treatments in cohort 2 vs cohort 1, although the observed difference was only significant for TAM. Conclusion In our center, a recent cohort of premenopausal women was more likely to be treated with the adjuvant endocrine treatment concordant with the guidance derived from the RCRS when using an arbitrary cut-off of 3 % to define a relevant improvement in outcome. Citation Format: Charlotte Berteloot, Patrick Neven, Maja Vangoitsenhoven, Annouschka Laenen, Hans Wildiers, Kevin Punie, Ann Smeets, Ines Nevelsteen, Sileny Han, Thaïs Baert, Hilde Janssen, Eva Oldenburger, Adinda Baten, Patrick Berteloot, Rani Vanhoudt, Anne Deblander, Chantal Remmeriev, Christine Desmedt. Real world adjuvant endocrine treatment in premenopausal breast cancer patients compared with the proposed algorithm using the Regan Composite Risk Score [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-02-04.