Breast Cancer Index and prediction of benefit from extended endocrine therapy based on treatment compliance: An IDEAL study.

531 Background: The IDEAL trial randomized hormone receptor-positive (HR+) breast cancer patients to 5 vs 2.5y of extended letrozole after completion of 5y of adjuvant endocrine therapy. In the parent trial, approximately 60% of patients overall were compliant with endocrine treatment (59% vs 74% compliance in 5y and 2.5y arms, respectively), with patient experiences as the most significant factors leading to treatment discontinuation. Breast Cancer Index is a gene expression-based signature that predicts which HR+ patients are likely to benefit from extended endocrine therapy (EET) vs those unlikely to benefit [BCI (H/I)-High and -Low, respectively]. The current study examined EET compliance and outcome by BCI (H/I) status in patients treated in the IDEAL trial. Methods: Patients with available primary tumor specimens were eligible for this blinded study. Primary endpoint was recurrence-free interval (RFI), including locoregional and distant recurrences. Kaplan-Meier and Cox proportional hazards regression analysis were used to analyze the benefit of EET. Non-compliance was defined as completion of ≤60% of treatment duration (≤3y for 5y arm; ≤1.5y for 2.5y arm) for any reason other than disease events. Overtreatment was defined as % compliant BCI (H/I)-Low patients in the 5y arm; undertreatment was % noncompliant BCI (H/I)-High patients in the 5y arm. Results: 908 HR+ patients (73% pN+, 59y, 45% pT1, 48% pT2) were included. 78% (n = 708) of patients were compliant, of which 48% (n = 338) were BCI (H/I)-High and 52% (n = 370) were BCI (H/I)-Low. In non-compliant patients (22%, n = 200), 45% (n = 91) were BCI (H/I)-High and 55% (n = 109) were BCI (H/I)-Low. BCI (H/I)-Low patients irrespective of compliance status did not derive significant benefit from EET (P = 0.922, compliant subset; 0.894 non-compliant subset). Compliant BCI (H/I)-High patients showed significant benefit from EET (HR 0.35, 95% CI 0.16-0.79; absolute benefit 11.7%; P = 0.008) whereas non-compliant BCI (H/I)-High patients did not (HR 0.75, 95% CI 0.17-3.35; absolute benefit 2.1%, P = 0.704). In this study, 38% of patients in the 5y EET arm were BCI (H/I)-Low and compliant and thus were overtreated, while 13% of patients in the 5y EET arm were BCI (H/I)-High and non-compliant and thus were undertreated. Conclusions: Patients that were BCI (H/I)-Low did not derive significant benefit from 5 vs 2.5y of EET even when compliant, and thus may be considered for treatment de-escalation. Importantly, BCI (H/I)-High patients with endocrine responsive disease showed significant improvements in outcome when compliant and should be guided to continue treatment. BCI may serve as an important genomic tool to increase EET compliance and identify patients that may be candidates for increased side effect management and support to potentially improve outcomes. Clinical trial information: NTR3077; BOOG 2006-05; Eudra-CT 2006-003958-16.

Molecular Drivers of Oncotype DX, Prosigna, EndoPredict, and the Breast Cancer Index: A TransATAC Study

PURPOSE The Onco type DX Recurrence Score (RS), Prosigna Prediction Analysis of Microarray 50 (PAM50) Risk of Recurrence (ROR), EndoPredict (EP), and Breast Cancer Index (BCI) are used clinically for estimating risk of distant recurrence for patients receiving endocrine therapy. Discordances in estimates occur between them. We aimed to identify the molecular features that drive the tests and lead to these differences. PATIENTS AND METHODS Analyses for RS, ROR, EP, and BCI were conducted by the manufacturers in the TransATAC sample collection that consisted of the tamoxifen or anastrozole arms of the ATAC trial. Estrogen receptor–positive/human epidermal growth factor receptor 2 (HER2)–negative cases without chemotherapy treatment were included in which all four tests were available (n = 785). Clinicopathologic features included in some tests were excluded from the comparisons. Estrogen, proliferation, invasion, and HER2 module scores from RS were used to characterize the respective molecular features. Spearman correlation and analysis of variance tests were applied. RESULTS There were moderate to strong correlations among the four molecular scores (ρ = 0.63-0.74) except for RS versus ROR (ρ = 0.32) and RS versus BCI (ρ = 0.35). RS had strong negative correlation with its estrogen module (ρ = −0.79) and moderate positive correlation with its proliferation module (ρ = 0.36). RS’s proliferation module explained 72.5% of ROR’s variance, while the estrogen module explained only 0.6%. Most of EP’s and BCI’s variation was accounted for by the proliferation module (50.0% and 54.3%, respectively) and much less by the estrogen module (20.2% and 2.7%, respectively). CONCLUSION In contrast to common understanding, RSs are determined more strongly by estrogen-related features and only weakly by proliferation markers. However, the EP, BCI, and particularly ROR scores are determined largely by proliferative features. These relationships help to explain the differences in the prognostic performance of the tests.