Abstract P2-03-18: Clinical use of Breast Cancer Index for prediction of late breast cancer recurrence and prediction of benefit in extended endocrine therapy: A single institution experience
Authors: Chacko Rebecca , Godbole Manasi M. , Springer Kylie , Ali Haythem , Dabak Vrushali 
Published: March 2023

Abstract
Background: The decision to extend adjuvant endocrine therapy beyond five years is often individualized. Breast Cancer Index (BCI) (Biotheranostics, Inc.) is a validated multigene-expression tissue-based analytic tool used in early hormone-positive breast cancer to predict the response to extended endocrine therapy, based on the HOXB13/IL17BR ratio (H/I ratio), and prognosis 5-10 years after diagnosis, based on the molecular grade index (MGI) and H/I ratio. It is presumed that if BCI shows a high likelihood of benefit from endocrine therapy (BCI-high), the treating clinician would recommend extended adjuvant endocrine therapy and if the primary prediction shows a low likelihood of benefit (BCI-low), the clinician would recommend discontinuation of therapy; however, this may not always be practiced. The Clinical Treatment Score post-5 years (CTS5) is a validated clinicopathologic tool that provides a calculated risk assessment of late distant recurrence (LDR). Clinicians may use the calculated CTS5 score in deciding whether to extend adjuvant endocrine therapy and forego additional prognostic testing, such as BCI. The aim of the study is to understand how clinicians integrate BCI results into medical decision making and to determine the correlation with CTS5 scores in making the decision to offer extended endocrine therapy. Methods: This is a single institution retrospective study. All patients within Henry Ford Health Systewho had BCI testing ordered, between April 2016 and January 2022, were included. Recommendations regarding extended endocrine therapy were collected. CTS5 scores were calculated based on patient’s age, tumor size, tumor grade, and number of involved lymph nodes. If available, the 21-gene recurrence scores (Oncotype-DX) and Ki-67 scores were collected for additional comparison. Results: A total of 165 female patients were included in this study. The average age at diagnosis was 58.5 ± 10.4 years old; 116 (70%) were Caucasian, 35 (21%) were African American; 132 patients (80%) were post-menopausal. The decision regarding extending endocrine therapy was concordant with BCI predictive results in 93.3% of patients; endocrine therapy was continued in 87% of patients in the BCI-high group and discontinued in 95% of patients in the BCI-low group (p&lt; 0.001). In comparing the categorical results of BCI predictive scores (low vs. high) and the CTS5 results (low vs. intermediate vs. high) univariate analysis did not detect a statistically significant relationship. In comparing BCI prognostic LDR risk percentage with the CTS5 LDR (5–10 year) risk percentage, a statistically significant, but weak, positive correlation was observed (Pearson correlation coefficient of 0.38487, p-value= &lt; 0.0001). The odds of a BCI-high primary prediction were 1.031 (95% CI: 1.005, 1.057) times higher for every-one percentage increase in Ki-67 (p-value=0.0172), 1.052 (95% CI: 1.003, 1.057) times higher for every one-unit increase in Oncotype-DX score (p-value=0.0353) and 1.232 (95% CI: 124, 1.351) times higher for every-one percentage increase in BCI prognostic LDR risk assessment (p-value &lt; 0.0001). No statistically significant association was found between the BCI predictive score and age, race, stage, lymph node involvement, and HER2 receptor positivity. Conclusions: This single-institution study revealed that clinicians make decisions regarding extended endocrine therapy that are usually concordant with BCI predictive results. CTS5 results weakly correlate with BCI prognostic results but may not provide conclusive information to support a clinical decision. For patients with early hormone-receptor positive breast cancer the BCI tissue-based analysis may influence a decision regarding extending endocrine therapy.
Citation Format: Rebecca Chacko, Manasi M. Godbole, Kylie Springer, Haythem Ali, Vrushali Dabak. Clinical use of Breast Cancer Index for prediction of late breast cancer recurrence and prediction of benefit in extended endocrine therapy: A single institution experience [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 P2-03-18.