Ultralow Risk Research Articles

Utility of the 70-Gene MammaPrint Assay for Prediction of Benefit From Extended Letrozole Therapy in the NRG Oncology/NSABP B-42 Trial.

MammaPrint (MP) determines distant metastatic risk and may improve patient selection for extended endocrine therapy (EET). This study examined MP in predicting extended letrozole therapy (ELT) benefit in patients with early-stage breast cancer (BC) from the NSABP B-42 trial. MP was tested in 1,866 patients randomly assigned to receive ELT or placebo. The primary end point was distant recurrence (DR). Secondary end points were disease-free survival (DFS) and BC-free interval (BCFI). Tumors were classified as MP high risk (MP-HR) or low risk (MP-LR). MP-LR tumors were further classified as ultralow risk (MP-UL) or low non-ultralow risk (MP-LNUL). There was no statistically significant difference in ELT benefit on DR between MP-HR and MP-LR (interaction P = .38). MP-LR tumors (n = 1,160) exhibited a statistically significant 10-year benefit of 3.7% for DR (hazard ratio [HR], 0.43 [95% CI, 0.25 to 0.74]; P = .002), whereas MP-HR tumors (n = 706) exhibited a nonsignificant 2.4% benefit (HR, 0.65 [95% CI, 0.34 to 1.24]; P = .19). The 10-year ELT benefit was significant for DFS (7.8%) and BCFI (7.0%) for MP-LR tumors, whereas MP-HR tumors did not significantly benefit (interaction DFS: P = .015, BCFI: P = .006). In exploratory analysis, the 10-year ELT benefit was significant and more pronounced in MP-LNUL (n = 908) tumors: 4.0% for DR, 9.5% for DFS, and 7.9% for BCFI; the benefit in MP-UL (n = 252) tumors was not significant: 3% for DR, 1.8% for DFS, and 4.1% for BCFI. The primary hypothesis of predictive ability of MP on DR was not confirmed. However, the secondary outcomes demonstrated MP was predictive of ELT response and identified a subset of patients with early-stage hormone receptor-positive BC (MP-LR) with improved outcomes from ELT. These data could have important clinical implications in patient selection beyond clinical risk assessment for EET.

Abstract PO1-02-11: Characterization of MammaPrint UltraLow Risk tumors in more than 1400 patients from the real-world evidence FLEX study

Abstract BACKGROUND: MammaPrint is a gene expression signature used to determine the risk of distant recurrence for patients with early-stage breast cancer. Previous studies from MINDACT, FOCUS, IKA, and STO-3 trials have demonstrated that postmenopausal node-negative patients with MammaPrint UltraLow Risk tumors are considered indolent and patients have excellent long-term survival outcomes up to 20 years with little to no endocrine treatment. These studies suggest that patients with UltraLow Risk tumors are ideal candidates for treatment optimization which has resulted in the inclusion of the UltraLow Risk result in the NCCN guidelines. Here, we characterized patients with UltraLow Risk tumors from the real-world evidence FLEX study. METHODS: FLEX (NCT03053193) is a prospective, observational registry study with 99 sites open in the United States, Canada, Greece, and Israel. Patients enrolled in FLEX have early-stage breast cancer and receive MammaPrint testing as standard of care (with or without BluePrint molecular subtyping), and consent to full transcriptome analysis and clinical data collection. MammaPrint is a gene expression signature of 70 genes that classifies tumors as having a Low Risk or High Risk of distant recurrence. Within Low Risk tumors, a subcategory of UltraLow Risk (MammaPrint Index > 0.355) has been defined in previous studies. Clinical data for this analysis was locked February 2023. Clinical risk was defined as low risk or high risk based on Adjuvant Online criteria. RESULTS: Among the 12,328 patients enrolled in FLEX, 1465 (11.9%) have UltraLow Risk tumors. All tumors with available BluePrint molecular subtyping were classified as Luminal-Type. Of the patients with detailed clinical data, the majority had clinically low risk tumors (78.8%; Table 1). Notably, 34.6% of patients with UltraLow Risk tumors had Ki67 tumor staining of greater than 10%, 16.7% were pre- or peri-menopausal, 43.6% had grade 2-3 tumors, and 20.1% had tumors > 2 cm (Table 1). Among patients with treatment information, 6.5% received a combination of chemotherapy with or without endocrine and HER2-targeted therapy, 82.4% received endocrine therapy, 4.8% received other treatment (endocrine with targeted therapy (CDK4/6), radiation alone, novel treatment regimen, or supporting agents), and 6.3% did not receive treatment (Table 1). CONCLUSIONS: Previous trials have demonstrated the utility of MammaPrint UltraLow Risk in patients with clinically low risk features. In this large real-world evidence study of patients with early-stage breast cancer, UltraLow Risk tumors can be identified across all clinical categories. Overall, we report a substantial number of premenopausal patients with UltraLow Risk tumors, and these young women would be good candidates for treatment optimization. Future studies will assess long-term outcomes in this cohort further stratified by treatment. Table 1. Clinical and genomic characteristics of UltraLow Risk tumors Data are presented as n (%). Patients with unknown or missing data for each category have not been included. Citation Format: Cathy Graham, Kent Hoskins, Vijayakrishna K. Gadi, Suzanne Hoekstra, Gordon Srkalovic, Douglas Marks, Beth Sieling, Patricia Dauer, Andrea Menicucci, William Audeh, Joyce O'Shaughnessy, FLEX Investigators' Group. Characterization of MammaPrint UltraLow Risk tumors in more than 1400 patients from the real-world evidence FLEX study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-02-11.

Ensemble-based classification using microRNA expression identifies a breast cancer patient subgroup with an ultralow long-term risk of metastases.

Current clinical markers overestimate the recurrence risk in many lymph node negative (LNN) breast cancer (BC) patients such that a majority of these low-risk patients unnecessarily receive systemic treatments. We tested if differential microRNA expression in primary tumors allows reliable identification of indolent LNN BC patients to provide an improved classification tool for overtreatment reduction in this patient group. We collected freshly frozen primary tumors of 80 LNN BC patients with recurrence and 80 recurrence-free patients (mean follow-up: 20.9 years). The study comprises solely systemically untreated patients to exclude that administered treatments confound the metastasis status. Samples were pairwise matched for clinical-pathological characteristics to minimize dependence of current markers. Patients were classified into risk-subgroups according to the differential microRNA expression of their tumors via classification model building with cross-validation using seven classification methods and a voting scheme. The methodology was validated using available data of two independent cohorts (n = 123, n = 339). Of the 80 indolent patients (who would all likely receive systemic treatments today) our ultralow-risk classifier correctly identified 37 while keeping a sensitivity of 100% in the recurrence group. Multivariable logistic regression analysis confirmed independence of voting results from current clinical markers. Application of the method in two validation cohorts confirmed successful classification of ultralow-risk BC patients with significantly prolonged recurrence-free survival. Profiles of differential microRNAs expression can identify LNN BC patients who could spare systemic treatments demanded by currently applied classifications. However, further validation studies are required for clinical implementation of the applied methodology.

Nomogram prediction of the 70-gene signature (MammaPrint) binary and quartile categorized risk using medical history, imaging features and clinicopathological data among Chinese breast cancer patients

BackgroundThe 70-gene signature (70-GS, MammaPrint) test has been recommended by the main guidelines to evaluate prognosis and chemotherapy benefit of hormonal receptor positive human epidermal receptor 2 negative (HR + /Her2−) early breast cancer (BC). However, this expensive assay is not always accessible and affordable worldwide. Based on our previous study, we established nomogram models to predict the binary and quartile categorized risk of 70-GS.MethodsWe retrospectively analyzed a consecutive cohort of 150 female patients with HR + /Her2− BC and eligible 70-GS test. Comparison of 40 parameters including the patients’ medical history risk factors, imaging features and clinicopathological characteristics was performed between patients with high risk (N = 62) and low risk (N = 88) of 70-GS test, whereas risk calculations from established models including Clinical Treatment Score Post-5 years (CTS5), Immunohistochemistry 3 (IHC3) and Nottingham Prognostic Index (NPI) were also compared between high vs low binary risk of 70-GS and among ultra-high (N = 12), high (N = 50), low (N = 65) and ultra-low (N = 23) quartile categorized risk of 70-GS. The data of 150 patients were randomly split by 4:1 ratio with training set of 120 patients and testing set 30 patients. Univariate analyses and multivariate logistic regression were performed to establish the two nomogram models to predict the the binary and quartile categorized risk of 70-GS.ResultsCompared to 70-GS low-risk patients, the high-risk patients had significantly less cardiovascular co-morbidity (p = 0.034), more grade 3 BC (p = 0.006), lower progesterone receptor (PR) positive percentage (p = 0.007), more Ki67 high BC (≥ 20%, p < 0.001) and no significant differences in all the imaging parameters of ultrasound and mammogram. The IHC3 risk and the NPI calculated score significantly correlated with both the binary and quartile categorized 70-GS risk classifications (both p < 0.001). The area under curve (AUC) of receiver-operating curve (ROC) of nomogram for binary risk prediction were 0.826 (C-index 0.903, 0.799–1.000) for training and 0.737 (C-index 0.785, 0.700–0.870) for validation dataset respectively. The AUC of ROC of nomogram for quartile risk prediction was 0.870 (C-index 0.854, 0.746–0.962) for training and 0.592 (C-index 0.769, 0.703–0.835) for testing set. The prediction accuracy of the nomogram for quartile categorized risk groups were 55.0% (likelihood ratio tests, p < 0.001) and 53.3% (p = 0.04) for training and validation, which more than double the baseline probability of 25%.ConclusionsTo our knowledge, we are the first to establish easy-to-use nomograms to predict the individualized binary (high vs low) and the quartile categorized (ultra-high, high, low and ultra-low) risk classification of 70-GS test with fair performance, which might provide information for treatment choice for those who have no access to the 70-GS testing.

LESS: Single-arm study to de-escalate adjuvant endocrine therapy duration in post-menopausal women with HR+ HER2- early-stage breast cancer at very low risk of metastasis.

TPS615 Background: Adjuvant Endocrine Therapy (ET) is the cornerstone treatment of localized hormone-receptor positive (HR+) breast cancer, with demonstrated benefits on overall survival (30-40% relative decrease in mortality) but also on the risk of local and contralateral relapse (43-50% relative decrease). While the relative benefit of 5 years of ET is identical for small tumors as compared to larger ones, the absolute benefit is much lower, and the risk-benefit ratio becomes questionable given the frequent and impactful side effects of ET which are associated with non-adherence. If recent trials tested longer durations as compared to 5 years for high-risk cancers, older trials have tested shorter durations. Five years appeared at that time as the gold standard because of optimal benefit-risk ratios of tamoxifen among rather high-risk patients. However, shorter treatments of 2-3 years were already associated with substantial benefits and may be enough for very low risk patients. The purpose of this study is to demonstrate that adjuvant ET limited to 2 years of aromatase inhibitor (AI) in postmenopausal women at very low risk of recurrence as determined with a MammaPrint and BluePrint Ultra Low Risk Luminal test result can ensure very high survival without metastatic relapse and allows a reduction of side effects and a better quality of life. Methods: LESS (NCT05297617) is a prospective, national, multicenter, single-arm, interventional, non-threshold crossing phase II study evaluating a therapeutic de-escalation that limits adjuvant ET to 2 years of AI. Approximately 696 post-menopausal patients with an invasive unilateral, HR+, HER2-negative, without indication of adjuvant chemoT and genomically-assessed MammaPrint/BluePrint UltraLow risk Luminal A breast cancer tumors, will be enrolled. LESS will include two sub cohorts: the majority of patients with Grade 2, pT1c-2, pN0/N1mic tumors, and up to 80 patients ≥65 years with Grade 1, pT1, pN0 and Ki67&lt;10% tumors. The primary endpoint is distant metastasis free survival (DMFS) defined as the time from date of registration to date of first event of distant recurrence, death, or second primary non-breast invasive cancer. Secondary endpoints include the assessment of quality of life parameters and psychological aspects related to this de-escalation. The null hypothesis (H0) that, in the study population after 2 years of adjuvant AI, DMFS at 5 years is lower or equal to 94.5% will be tested against the alternative - that it is above 94.5%. For an expected DMFS of 96.7% under the alternative hypothesis, a total of 37 DMFS events are required in order to provide approximately 85% power at a one-sided significance level of 0.05 to reject H0 using a logrank test. The 1st patient was included in October 2022, initiating the 2-year inclusion period and 10 years FU per patient. Clinical trial information: NCT05297617 .

Cost-Effectiveness Analysis of MammaPrint® to Guide the Use of Endocrine Therapy in Patients with Early-Stage Breast Cancer.

Gene expression profiling tests can predict the risk of disease recurrence and select patients who are expected to benefit from therapy, while allowing other patients to forgo therapy. For breast cancers, these tests were initially designed to tailor chemotherapy decisions, but recent evidence suggests that they may also guide the use of endocrine therapy. This study evaluated the cost effectiveness of a prognostic test, MammaPrint®, to guide the use of adjuvant endocrine therapy in patients eligible according to Dutch treatment guidelines. We constructed a Markov decision model to calculate the lifetime costs (in 2020 Euros) and effects (survival and quality-adjusted life-years) of MammaPrint® testing versus usual care (endocrine therapy for all patients) in a simulated cohort of patients. The population of interest includes patients for whom MammaPrint® testing is currently not indicated, but for whom it may be possible to safely omit endocrine therapy. We applied both a health care perspective and a societal perspective and discounted costs (4%) and effects (1.5%). Model inputs were obtained from published research (including randomized controlled trials), nationwide cancer registry data, cohort data and publicly available data sources. Scenario and sensitivity analyses were conducted to explore the impact of uncertainty around input parameters. Additionally, threshold analyses were performed to identify under which circumstances MammaPrint® testing would be cost effective. Adjuvant endocrine therapy guided by MammaPrint® resulted in fewer side effects, more (quality-adjusted) life-years (0.10 and 0.07 incremental QALYS and LYs, respectively) and higher costs (€18,323 incremental costs) compared with the usual care strategy in which all patients receive endocrine therapy. While costs for hospital visits, medication costs and productivity costs were somewhat higher in the usual care strategy, these did not outweigh costs of testing in the MammaPrint® strategy. The incremental cost-effectiveness ratio was €185,644 per QALY gained from a healthcare perspective and €180,617 from a societal perspective. Sensitivity and scenario analyses showed that the conclusions remained the same under changed input parameters and assumptions. Our results show that MammaPrint® can become a cost-effective strategy when either the price of the test is reduced (>50%), or the proportion of patients for which treatment is altered (i.e. those with ultra-low risk) increases to >26%. Standard MammaPrint® testing to guide the use of endocrine therapy in our simulated patient population appears not to be a cost-effective strategy compared with usual care. The cost effectiveness of the test can be improved by reducing the price or preselecting a population more likely to benefit from the test.

Validation of the 70-gene signature test (MammaPrint) to identify patients with breast cancer aged ≥70 years with ultralow risk of distant recurrence: A population-based cohort study

Validation of the 70-gene signature test (MammaPrint) to identify patients with breast cancer aged ≥70 years with ultralow risk of distant recurrence: A population-based cohort study

115P Longterm prognostic utility of 70-gene signature by clinical and genomic risks, including Ultralow (gUL) risk patients (pts)

In the MINDACT trial, 4 risk categories (RC) by clinical (c) and genomic (g) risks were defined. In cHigh/gLow risk patients (pts) with no adjuvant chemotherapy (CT), 8y-Distant Metastases Free Survival (DMFS) was 89.4 % [95% CI 86.2-91.5]. MP also identified a third subgroup of gUL pts (score 0.355 – 1.0, 15% in MINDACT), with an excellent prognosis and no benefit from extended endocrine therapy (EET). We aimed to study: DFS/ DMFS by the 6 RC resulting from combining the 2 (c) categories with the 3 (g) groups; the timing of recurrences; and the putative benefit of EET for each genomic group. All ER+/HER2- BC pts with MP data diagnosed between 2012-2017 at Vall d'Hebron University Hospital were selected. cLow risk was defined as in MINDACT trial. To study the benefit of EET, a landmark analysis at 5y from ET initiation was conducted. 140 pts were identified. Baseline features: 47.8% premenopausal; stage I/II: 74%/26%; histological grade 1/2/3: 19.6%/74.9%/6.5%. cLow/cHigh: 67%/33%; gUL/gLow-Non-Ultralow (LNUL)/gHigh: 11.4%/53.6%/35%. PgR and Ki67 tended to correlate with MP g risks, but only the IHC-subtype reached statistically significance. Systemic adjuvant treatments [N/%]: ET 138/98.5%; ovarian function suppression for premenopausal pts 23/35%; CT: 45/32%; EET: 49/35.8%. After 8y-median FU, 15 DFS events and 11 DMFS were observed. DMFS in cHigh/gLow (UL+LNUL) without CT was 90.6% [81.1%; 100%]. DFS/DMFS rates by each c/g category are depicted in the table. Only 4 DMFS events occurred after 5 years, precluding to explore EET role by RCTable: 115PcLow-gULcLow-gLNULcLow-gHighcHigh-gULcHigh-gLNULcHigh-gHighN (%)13 (9.4)45 (32)35 (25)3 (2.2)30 (22)13 (9.4)8y-DFS (%)1009184.81009076.9CI 95%-83.2-99.871.6-100-79.9-10057.1-1008y-DMFS (%)10095.589.11009084.6CI 95%-89.6-10077.7-100-79.9-10067.1-1008y-DMFS (%)cHigh-gLow (UL+LNUL) No CT90.6% (CI 95% 81.1-100)8y-DMFS (%) in Mindact TrialcHigh-gLow (UL+LNUL) No CT89.4% (CI 95% 86.2-91.5) Open table in a new tab . In our series, DMFS rate in cHigh-gLow pts without CT was similar to that reported in MINDACT trial. In line with prior reports, gUL pts had excellent survival, while cHigh-gHigh group showed significantly poorer outcome. Albeit limited by small sample size, classification in 6 RCs instead of 4 seems useful to redefine prognosis. Additional FU is warranted to determine the EET benefit in each RC.

Abstract GS5-10: Utility of the 70-gene MammaPrint test for prediction of extended endocrine therapy benefit in patients with early-stage breast cancer in the IDEAL Trial

Abstract Background: The IDEAL trial showed no significant benefit of 5 years extended endocrine therapy (EET) using letrozole in postmenopausal patients with hormone receptor positive (HR+) breast cancer (BC) versus 2.5 years. Genomic classifiers may assist with treatment decisions by predicting EET benefit. The 70-gene MammaPrint (MP) test classifies tumors as having a higher or lower risk of distant metastasis in HR+ early-stage BC. A MP lower risk result can be further classified as either Ultra-Low risk or Low risk of distant metastasis. In the NSABP B42 trial, MP predicted a statistically significant absolute benefit from EET in patients with a MP Low Risk result. Here, we aimed to determine the utility of MP in identifying a subgroup of patients enrolled in the IDEAL trial for which 5 years of EET is beneficial compared to 2.5 years. Methods: A total of 869 patients had available primary tumor tissue for testing. MP results were available for 545/869 patients, of which 515 did not have an event at 2.5 year after randomization and were used for our analyses. The MP result for each patient was calculated by Agendia while blinded to patient clinical outcomes. The primary endpoint was distant recurrence (DR). Secondary endpoints were recurrence free interval (RFI) and breast cancer free interval (BCFI) as defined by STEEP criteria. Patients were classified as higher risk (score -1.000 - 0) or lower risk (score 0.001 - 1.000). Lower risk tumors were further classified as either MP Ultra-Low (score &amp;gt; 0.355) or MP Low Risk (score ≥ 0.001, ≤ 0.355). Likelihood ratio test based on stratified Cox proportional hazards (PH) model were used to evaluate treatment by risk group interaction. Differences in endpoints between treatment groups were assessed by stratified log-rank tests. Hazard ratios (HR) and 95% Confidence Intervals (CI) were computed based on the stratified Cox PH model. Results: The clinical characteristics of the 515 IDEAL samples with a MP result were comparable to the whole IDEAL cohort (n=1820). Within the 2.5 year EET group, 50.6% (n=134) were MP higher risk and 49.4% (n=131) MP lower risk, of which 14.5% (n=19/131) were MP Ultra-Low. Within the 5 year EET group, 50.0% (n=125) were MP higher risk and 50.0% (n=125) MP lower risk, of which 11.2% (n=14/125) were MP Ultra-Low. Among patients with MP lower risk tumors, 5 years vs. 2.5 years of EET resulted in a significant absolute benefit of 9.8% for DR (HR=0.42, [95% CI 0.174-0.996]), 9.8% for RFI (HR=0.43, [95% CI 0.198-0.934]), and 8.8% (HR=0.53, [95% CI 0.264-1.055]) for BCFI, whereas patients with MP higher risk tumors did not derive significant benefit (Table 1). Within the MP lower risk group, 5 year vs 2.5 year EET benefit was more pronounced in MP Low tumors, which exhibited a significant benefit of 10.1% for DR (HR=0.32, [95% CI 0.116-0.866]), 11.7% for RFI (HR=0.35, [95% CI 0.147-0.824]), and 9.7% for BCFI (HR=0.48, [95% CI 0.225-1.015]); MP Ultra Low tumors did not derive significant benefit. Treatment-by-risk group interaction was statistically significant for RFI. Conclusion: A significant EET benefit was observed for MammaPrint lower risk tumors but not for MP higher risk tumors. MammaPrint Low tumors exhibited the largest absolute benefit of 5 years of EET compared to 2.5 years. Consistent with the findings in the NSABP B42 trial, the results from this second randomized trial provide clinically meaningful implications in patient selection for extended endocrine therapy. Table 1. IDEAL: 10-year outcome analysis comparing 5 years vs. 2.5 years of EET using letrozole stratified by MP risk. **MammaPrint Lower Risk &amp; Higher Risk (n=515) and *** MammaPrint Low Risk &amp; High Risk (n=482) Citation Format: Gerrit-Jan Liefers, Elma Meershoek-Klein Kranenbarg, Marjolijn Duijm-de Carpentier, Cornelis J.H. van de Velde, Miranda Kleijn, Christa Dreezen, Andrea Menicucci, Laura van’t Veer, William Audeh. Utility of the 70-gene MammaPrint test for prediction of extended endocrine therapy benefit in patients with early-stage breast cancer in the IDEAL Trial [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 GS5-10.

Abstract P3-05-44: Genomic testing and Ki-67 Percentage: Two puzzle pieces being undervalued in breast cancer treatment

Abstract Background: Genetic resources are underutilized when it comes to being incorporated into a breast cancer patient’s treatment, but that isn’t the only piece being overlooked. The Ki-67 proliferation index expressed (Ki-67%) is an established marker of tumor proliferation and aggressive behavior. We hypothesized that Ki-67% could have increased clinical utility when correlated with genomic testing results. Methods: Data was obtained from the Informed Genetics Annotated Patient Registry (iGAP), an IRB-approved, multi-center longitudinal registry designed to capture biomarker test results and their impact on treatment practices and outcomes. Tumor grades and Ki-67% were taken from patient pathology reports. The average Ki-67% was then calculated and compared for each tumor grade, MammaPrint genomic recurrence risk category (ultra low risk, low risk, and high risk), and Blueprint molecular subtype (Luminal type A, Luminal type B, Basal, and HER 2 type). ANOVA statistical analysis was performed for significance values. Results: Of 3102 patients enrolled in the iGAP Registry, 733 were diagnosed with breast cancer and had available tumor grade and Ki-67% data. Among these patients, 357 had genomic recurrence risk (MammaPrint) and 220 genomic molecular subtyping (BluePrint) reports. As expected, tumor grades were significantly positively correlated with Ki-67% (p&amp;lt; 0.0001 between all 3 tumor grade groups). Average Ki-67% in each genomic recurrence risk revealed a significant difference between Low Risk (14%, range 1-70%) and High Risk (36%, range 1-95%, p&amp;lt; 0.0001). Among the genomic molecular subtypes, there were significant differences in Ki-67% between Basal (avg 69%, 17-95%) and Luminal type A (avg 13%, 1-70%, p&amp;lt; 0.0001)) and all other subtypes, while Luminal type B (avg 24%, 1-80%) and HER 2 (avg 38%, 29-45%) were not significantly different from each other (p=0.2817), but still significantly different to all other subtypes. Conclusion: From these results, we can deduce that molecular subtype correlates with, but is clinically distinct from, Ki-67 proliferation index. These results also indicate that molecular subtype correlates with higher tumor grades, possibly due to increased cell proliferation. Achieving truly personalized clinical decision making requires utilizing multiple modalities and biomarkers, integrating the results into management. Citation Format: Chloe Wernecke, Krista Ortega, Kelly Bontempo, Brenna Bentley, Christina Hoyer-Kimura, Peter Beitsch, Rakesh Patel, Barry Rosen, Gia Compagnoni, Ian Grady, Eric Brown, Lindsay Gold, Pat Whitworth, Linda Ann Smith, Richard Reitherman, Mariusz Wirga, Steven Cai, Toan Nguyen, Valerie Traina, Dennis Holmes, Paul Baron, Brittany Krautheim, Anne Peled, Walt Taylor. Genomic testing and Ki-67 Percentage: Two puzzle pieces being undervalued in breast cancer treatment [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 P3-05-44.

Abstract P4-02-20: Utility of the 70-gene signature and 10 year follow up in patients with early-stage breast cancer in a single institution study

Abstract Introduction: Genomic tests are routinely used by clinicians to guide treatment decisions in early-stage breast cancer (EBC). The 70-gene MammaPrint assay (MP) assesses the risk of distant recurrence in untreated patients with EBC and categorizes the tumors as High Risk (HR, MP index: -1 to ≤0) or Low Risk (LR, &amp;gt;0 to +1). The LR category is further divided into Low but non-UltraLow (LNUL; &amp;gt;0 to ≤0.355) and UltraLow Risk (UL; &amp;gt;0.355 to 1). Here, we report the risk of distant recurrence by MP and 10-year outcomes in patients with EBC diagnosed at Magee Women’s Hospital of the University of Pittsburgh Medical Center. Methods: In this retrospective analysis, 259 women diagnosed with EBC between 2005 and 2008, who received a MP result, were included. Patient clinical and tumor characteristics were collected. The median FU was 13.1 year among patients with clinical data. Treatment received, 10-year Distant Metastasis Free Interval (DMFI) and 10-year Breast Cancer Specific Survival (BCSS) are reported according to the MP groups. Differences in DMFI and BCSS between MP risk groups were assessed by log-rank. Patients were treated at the physician’s discretion. Treatment was started prior to obtaining MammaPrint results. Results: Among the 259 patients, 69% were post-menopausal women (mean [range] age: 58 [31-81] years) and diagnosed with hormone receptor-positive HER2-negative tumors (90%), grade 1 or 2 (64%), and without lymph node invasion (93%). In this cohort, 69% (n = 159) had a MP LR result and 31% (n = 100) had a MP HR result. Overall, 14% (n = 35) of patients had a MP UL risk of recurrence of whom 74% (n = 26/35) were post-menopausal women. Substantially more patients received chemotherapy in the HR group (57%, n = 57) compared with the LR group (15%, n = 24) (table). Considering that treatment was initiated before MammaPrint results were known, MP results might have allowed chemotherapy de-escalation in in 15% (n = 24) of patients with a MP LR. Similarly, in the 39% (n = 39) of women with a MP HR treated with endocrine therapy only, knowledge of MP results could have provided important information to add chemotherapy to the treatment plan.. In the MP UL group, 74 % (n = 26) of patients were treated with endocrine therapy only compared with those who received chemotherapy (9%, n = 3) and no adjuvant treatment (9%, n = 3). The 10-year DMFI and 10-year BCSS were higher in the LR compared with the HR group (table). When further stratifying the MP LR group in LNUL and UL, the 10y DMFI was 0.97 (95% CI; 0.94 – 1.00) and 1.00 for the MP LNUL and UL groups, respectively. Within the first 10 years, 8 of the 10 distant recurrences observed were in the MP HR group, and 2 were in the MP LNUL group. Among the 18 recorded deaths, 5 were breast cancer-related, 4 in the MP HR and 1 in the MP LR (LNUL) groups. Discussion: In this single-institution retrospective analysis, all patients showed excellent BCSS and DMFI outcomes confirming the ability of MP to correctly predict the good prognosis (LR) and poor prognosis (HR) in patients with EBC. In this analysis, as observed in other cohorts, women with a MP UL risk result had an excellent prognosis at 10 years while being treated mostly with endocrine therapy only. Taken together, with the low endocrine therapy adherence reported in the literature, these data suggest that patients with a MP UL result may be candidates for further treatment de-escalation to optimize the risk/benefit ratio of endocrine therapy in future studies. Table 1. Clinical outcomes and treatment received in patients stratified by MammaPrint results * Patients were treated at the physician’s discretion a p = 0.011, MP LR vs MP HR. b p = 0.032, MP UL vs LNUL vs HR. c p = 0.061 MP LR vs MP HR. d p = 0.170, MP UL vs LNUL vs HR. Citation Format: Azadeh Nasrazadani, Juan L. Gomez Marti, Margaret Q. Rosenzweig, Meghan McGuire, Katie Quinn, Josien Haan, Alexandre Houzelle, Rohit Bhargava, William Audeh, Adam M. Brufsky. Utility of the 70-gene signature and 10 year follow up in patients with early-stage breast cancer in a single institution study [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 P4-02-20.

Abstract B027: PIK3CA hotspot mutations as biomarkers for prognosis and treatment prediction in low-risk postmenopausal breast cancer patients

Abstract The PIK3CA gene, encoding the p110α catalytic subunit of PI 3-kinase (PI3K), is mutated in more than 30% of breast cancers. Most mutations concentrate to the hotspots E542K and E545K and H1047R and are associated with hyperactivation of the phosphatidylinositol 3′-kinase/Akt pathway in vitro. The estrogen receptor-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2-) (ER+/HER2-) breast cancers stand for more than 40% of the PIK3CA mutations where these constitute a new therapeutic target for endocrine-treatment resistant advanced breast cancers. Although PIK3CA is an oncogene, its mutations are associated with good prognosis. Here, we explored the prognostic and predictive role of PIK3CA hotspot mutations for low-risk postmenopausal breast cancer patients randomized to receive tamoxifen vs. no systemic treatment, followed for over 25 years and with extensive clinical records. Mutation analysis was performed using formalin-fixed paraffin-embedded tumors with digital droplet PCR (ddPCR). PIK3CA mutations were present in 35,6% of patients, predominantly within the ER+/HER2- subtype (49,8%) compared with the HER2+ and TNBC subtypes. The most frequent mutation found in all patients was H1047R (18%) followed by E545K (14%) and E542K (6%). Significant associations were found between all hotspot mutations and low grade, positive progesterone receptor (PR) expression, HER2 negative status, low Ki-67 (proliferation marker), and high expression score of a PIK3CA-mutation-associated gene module. Moreover, PIK3CA mutations were often found in patients with ultralow risk to develop distant recurrences according to the 70-gene signature. All PIK3CA mutations were coupled with longer distant recurrence-free interval (DRFI) in all patients in univariate and multivariable analysis after adjusting for tumor size, receptor status (ER, PR, HER2), tumor grade, Ki-67 and tamoxifen: HR multivariable (95% CI)=0.53 (0.28-0.98). In agreement with our previous results, PIK3CA mutations indicated good prognosis for patients with highly proliferative tumors (Ki-67&amp;gt;15%): H.R multivariable (95% CI)=0.15 (0.03-0.69) and high risk by the 70-gene signature: HR multivariable (95% CI)=0.14 (0.03-0.61) but not for low proliferative tumors (Ki-67&amp;lt;15%). In fact, PIK3CA mutations indicated adverse prognosis within those patients with ultralow risk where the registered survival was 100% in presence of the PIK3CA wild type genotype. PIK3CA mutations did not have predictive value for tamoxifen. In conclusion, PIK3CA mutations predominate within the ER+/HER2- subtype, are coupled with good clinical markers and longer DRFI in all patients and especially among aggressive tumors but not in ultralow risk patients. Further investigation will be needed to decipher the role of PIK3CA in patients with ultralow risk or indolent tumors who may present long-term relapses and specially benefit from PI3K inhibition. Citation Format: Carolin Jönsson, Zeinab Alkashaf, Josefine Sandström, Annelie Johansson, Tommy Fornander, Linda S. Lindström, Gizeh Perez Tenorio. PIK3CA hotspot mutations as biomarkers for prognosis and treatment prediction in low-risk postmenopausal breast cancer patients [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr B027.

Clinicopathological characteristics and survival results of patients with ultralow risk breast cancer

Background and objectiveTo identify subgroups with good progress over an extended period, we used diagnostic screening, tumour palpability, tumour phenotype, and node involvement. Patients and methodsWe identified patients with good progress by means of a descriptive, observational and retrospective study. ResultsOf 746 patients diagnosed with node-negative breast cancer between 2001 and 2015: 110 (14.75%) had non-palpable screening-diagnosed tumours; 88 (80%) were endocrine-sensitive, 10 (9.10%) were triple-negative and 11 (10%) were HER2. Only 3 patients developed metastases, and there were 4 deaths: 2 from breast cancer and 2 from other causes. The distant recurrence-free interval (DRFI) was 95.60%: 100% in 34 endocrine-sensitive histological grade 1 (equivalent to luminal A) tumours, and 94.40% (95% CI 86.76–102.04) in 54 grade 2–3 (luminal B) tumours. In triple-negative and HER2 cases, it was 100%. In tumours <1 cm it was 100%, and >1 cm it was 95.50% (95% CI 79.42–100.98). ConclusionPatients with non-palpable tumours detected by mammogram screening have ultralow risk. The good progress in the luminal A, triple-negative, HER2, and less than 1 cm subgroups may explain the efficacy of the treatment but it also makes them candidates to de-escalation of their treatment.

Validation of the 70-gene signature test (MammaPrint) to identify patients with breast cancer aged ≥ 70 years with ultralow risk of distant recurrence: A population-based cohort study

IntroductionWhen risk estimation in older patients with hormone receptor positive breast cancer (HR + BC) is based on the same factors as in younger patients, age-related factors regarding recurrence risk and other-cause mortality are not considered. Genomic risk assessment could help identify patients with ultralow risk BC who can forgo adjuvant treatment. However, assessment tools should be validated specifically for older patients. This study aims to determine whether the 70-gene signature test (MammaPrint) can identify patients with HR + BC aged ≥70 years with ultralow risk for distant recurrence. Materials and MethodsInclusion criteria: ≥70 years; invasive HR + BC; T1-2N0-3M0. Exclusion criteria: HER2 + BC; neoadjuvant therapy. MammaPrint assays were performed following standardized protocols. Clinical risk was determined with St. Gallen risk classification.Primary endpoint was 10-year cumulative incidence rate of distant recurrence in relation to genomic risk. Subdistribution hazard ratios (sHR) were estimated from Fine and Gray analyses. Multivariate analyses were adjusted for adjuvant endocrine therapy and clinical risk. ResultsThis study included 418 patients, median age 78 years (interquartile range [IQR] 73–83). Sixty percent of patients were treated with endocrine therapy. MammaPrint classified 50 patients as MammaPrint-ultralow, 224 patients as MammaPrint-low, and 144 patients as MammaPrint-high risk. Regarding clinical risk, 50 patients were classified low, 237 intermediate, and 131 high. Discordance was observed between clinical and genomic risk in 14 MammaPrint-ultralow risk patients who were high clinical risk, and 84 patients who were MammaPrint-high risk, but low or intermediate clinical risk. Median follow-up was 9.2 years (IQR 7.9–10.5).The 10-year distant recurrence rate was 17% (95% confidence interval [CI] 11–23) in MammaPrint-high risk patients, 8% (4–12) in MammaPrint-low (HR 0.46; 95%CI 0.25–0.84), and 2% (0–6) in MammaPrint-ultralow risk patients (HR 0.11; 95%CI 0.02–0.81). After adjustment for clinical risk and endocrine therapy, MammaPrint-high risk patients still had significantly higher 10-year distant recurrence rate than MammaPrint-low (sHR 0.49; 95%CI 0.26–0.90) and MammaPrint-ultralow patients (sHR 0.12; 95%CI 0.02–0.85). Of the 14 MammaPrint-ultralow, high clinical risk patients none developed a distant recurrence. DiscussionThese data add to the evidence validating MammaPrint's ultralow risk threshold. Even in high clinical risk patients, MammaPrint-ultralow risk patients remained recurrence-free ten years after diagnosis. These findings justify future studies into using MammaPrint to individualize adjuvant treatment in older patients.

Clinical implications for patients with discordant oncotype and MammaPrint results.

560 Background: Genomic tests provide critical information regarding risk of recurrence and inform treatment plans by identifying those patients who may safely forgo chemotherapy (CT) or shorten endocrine therapy (ET) duration. The IMPACT trial demonstrated that the 70 -gene risk of recurrence assay MammaPrint (MP) and 80-gene subtyping assay BluePrint (BP) inform treatment planning and increase physician confidence. However, not all genomic tests yield the same results. To examine consistency among genomic tests, we analyzed therapy implications for patients who received results from both MP/BP and Recurrence Score (RS). Methods: Using the FLEX cohort (NCT03053193), we examined 723 patients who received both MP/BP, and RS genomic assays. We assessed the potential clinical impact by examining the standardized reports of RS and MP/BP results. MP classified tumors as either ultralow, low, or high risk and BP further classified them as luminal, basal, or HER2. RS classified tumors as low (RS0-10), intermediate (RS11-25), or high (RS26-100). Clinical impact was defined as discordant genomic resulting in different treatment recommendations. Undertreatment indicates patients who may not have received CT based on RS but may have based on MP/BP and overtreatment those patients who would have received CT based on RS, but not based on MP/BP. ET duration too long is indicative of those patients that are ultralow risk by MP, regardless of RS classification, as those patients may have safely reduced the duration of their ET. Although outcomes are not available, treatment impacts are presuming a patient received both tests, but the treating physician opted to guide therapy according to the RS results rather than MP/BP. Results: We observed discordant results with a clinical impact in 49% (354) of patients, with 34% (244) who may be undertreated, 2% (11) potentially overtreated, and 14% (99) who may not be given the option to decrease ET to two years based on ultralow MP genomic risk. Of 114 concordant High-Risk tumors, 14% (16) were genomically Basal, and likely to require more aggressive CT than typically used in ER+ cancers. The table below summarizes the results. Conclusions: More than half of the patients in this cohort were at potential risk for undertreatment or overtreatment. The risk to patients is far more significant in the event of undertreatment, as this may result in incurable metastatic recurrence. Discordance between RS and MP/BP most often results in potential undertreatment if RS is used for treatment decision-making. Clinical trial information: NCT03053193.

Clinical and molecular characteristics of estrogen receptor-positive ultralow risk breast cancer tumors identified by the 70-gene signature.

The metastatic potential of estrogen receptor (ER)‐positive breast cancers is heterogeneous and distant recurrences occur months to decades after primary diagnosis. We have previously shown that patients with tumors classified as ultralow risk by the 70‐gene signature have a minimal long‐term risk of fatal breast cancer. Here, we evaluate the previously unexplored underlying clinical and molecular characteristics of ultralow risk tumors in 538 ER‐positive patients from the Stockholm tamoxifen randomized trial (STO‐3). Out of the 98 ultralow risk tumors, 89% were luminal A molecular subtype, whereas 26% of luminal A tumors were of ultralow risk. Compared to other ER‐positive tumors, ultralow risk tumors were significantly (Fisher's test, P < .05) more likely to be of smaller tumor size, lower grade, progesterone receptor (PR)‐positive, human epidermal growth factor 2 (HER2)‐negative and have low Ki‐67 levels (proliferation‐marker). Moreover, ultralow risk tumors showed significantly lower expression scores of multi‐gene modules associated with the AKT/mTOR‐pathway, proliferation (AURKA), HER2/ERBB2‐signaling, IGF1‐pathway, PTEN‐loss and immune response (IMMUNE1 and IMMUNE2) and higher expression scores of the PIK3CA‐mutation‐associated module. Furthermore, 706 genes were significantly (FDR < 0.001) differentially expressed in ultralow risk tumors, including lower expression of genes involved in immune response, PI3K/Akt/mTOR‐pathway, histones, cell cycle, DNA repair, apoptosis and higher expression of genes coding for epithelial‐to‐mesenchymal transition and homeobox proteins, among others. In conclusion, ultralow risk tumors, associated with minimal long‐term risk of fatal disease, differ from other ER‐positive tumors, including luminal A molecular subtype tumors. Identification of these characteristics is important to improve our prediction of nonfatal vs fatal breast cancer.

Características clínico-patológicas y supervivencia de pacientes con cáncer de mama de riesgo muy bajo

Background and objectiveTo identify subgroups with good progress over an extended period, we used diagnostic screening, tumour palpability, tumour phenotype, and node involvement. Patients and methodsWe identified patients with good progress by means of a descriptive, observational and retrospective study. ResultsOf 746 patients diagnosed with node-negative breast cancer between 2001 and 2015: 110 (14.75%) had non-palpable screening-diagnosed tumours; 88 (80%) were endocrine-sensitive, 10 (9.10%) were triple-negative and 11 (10%) were HER2. Only 3 patients developed metastases, and there were 4 deaths: 2 from breast cancer and 2 from other causes. The distant recurrence-free interval (DRFI) was 95.60%: 100% in 34 endocrine-sensitive histological grade 1 (equivalent to luminal A) tumours, and 94.40% (95% CI 86.76–102.04) in 54 grade 2–3 (luminal B) tumours. In triple-negative and HER2 cases, it was 100%. In tumours <1 cm it was 100%, and >1 cm it was 95.50% (95% CI 79.42–100.98). ConclusionsPatients with non-palpable tumours detected by mammogram screening have ultralow risk. The good progress in the luminal A, triple-negative, HER2, and less than 1 cm subgroups may explain the efficacy of the treatment but it also makes them candidates to de-escalation of their treatment.

Abstract P1-02-12: Genomic testing on breast cancer core biopsy material is feasible and provides useful treatment information

Abstract Background: Genomic profiling assays for invasive breast cancer provide useful predictive and prognostic information and are performed most commonly on surgical resection specimens. Obtaining the molecular profile at the time of initial core needle biopsy is ideal because it could provide information that could significantly alter preoperative decision-making and avoid unnecessary treatments. In January 2020, the breast center began a 3 month pilot program that would reflexively send core biopsy material on all newly diagnosed patients for genomic testing using the MammaPrint (MPT) and BluePrint (BPT) assays regardless of receptor status. The goals were to determine feasibility and examine the impact to patient care. Methods: Breast core biopsy tissue was triaged by an attending pathologist as soon as slides were available. If invasive carcinoma with at least 3 mm in linear extent of tumor with 20% cellularity was identified, materials were immediately sent to Agendia for MPT/BPT testing even before ER/PR/HER2 testing was available to the pathologist. Clinicopathologic information, turn-around time (TAT) and adequacy data were tracked. The impact was discussed regularly at breast tumor board to determine if the results led to altered decision-making that could reduce unnecessary interventions and time to initial treatment. Results: 445 core biopsy specimens were sent for genomic testing. Of those 442, (97%) yielded genomic results with an average TAT from biopsy to genomic result of 11 calendar days. MPT identified 233 (53%) cases that were low risk and 209 (47%) cases that were high risk. BPT showed that 60 (14%) cases were Basal, 18 (4%) cases were HER2, and 364 (82%) cases were Luminal. Further analysis of the Luminal subgroup demonstrated that 154 (42%) were Luminal A low risk, 78 (21%) were Luminal A Ultralow risk and 132 (36%) were Luminal B High Risk. Analysis by race demonstrated a significantly higher percentage of high risk tumors in African-American women including a higher percentage of basal cancers (26%) as compared to Caucasian women (10%). Of note, 51 patients in the pilot study had additional OncotypeDX (ODX) testing on subsequent surgical resection. There was fair correlation between the assays with the majority of the low risk MPT having low risk ODX scores (&amp;lt;=25) and the high risk MPT having high risk ODX scores (&amp;gt;25), though MPT identified more patients as being high risk. The COVID-19 pandemic altered plans to assess time to treat and treatment interventions as initially intended. However, the knowledge of genomic result enhanced the ability to triage patients, allowing those patients with low risk tumors to begin endocrine therapy and delay surgery. Use of preoperative hormone therapy was considered more often in place of neoadjuvant chemotherapy in patients with low genomic risk ER+/HER2- patients. Because of the continued feedback indicating positive impact, the pilot ultimately was extended to 11 months to allow time for formal implementation. Conclusions: Genomic testing using the MPT/BPT assay on core biopsy samples with at least 3 mm yields results 97% of the time with an average TAT of 11 days from biopsy date to result. The genomic information at the time of initial diagnosis impacted patient care most notably in the ER+ setting. The results led to the immediate implementation of direct reflex testing of all newly diagnosed ER+ and HER2- or IHC 2+ cancers by pathology after the initial pilot phase. Citation Format: Hannah Gilmore, Philip Bomeisl, Alberto Montero. Genomic testing on breast cancer core biopsy material is feasible and provides useful treatment information [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-02-12.

Outcome of Patients With an Ultralow-Risk 70-Gene Signature in the MINDACT Trial.

Patients with 70-gene signature ultralow-risk breast cancers have shown excellent survival in historic cohorts, including randomized trials. The ultralow-risk subgroup was characterized to help avoid overtreatment. We evaluated outcomes of ultralow-risk patients in the largest cohort to date. Of the 6,693 patients enrolled in the EORTC-10041/BIG-3-04 randomized phase III MINDACT trial, profiling revealed an ultralow-risk 70-gene signature in 1,000 patients (15%). Distant metastasis-free interval (DMFI) and breast cancer-specific survival (BCSS) were assessed in patients stratified by 70-gene signature result (high, low, and ultralow) by Kaplan-Meier analysis and hazard ratios with 95% CI from Cox regression. Median follow-up was 8.7 years. Of the ultralow-risk patients (n = 1,000), 67% were > 50 years, 81% had tumors ≤ 2 cm, 80% were lymph node-negative, 96% had grade 1 or 2 tumors, and 99% were estrogen receptor (ER)-positive. Systemic therapy was received by 84% of patients (69% endocrine therapy, 14% endocrine therapy plus chemotherapy, 1% other) and 16% received no adjuvant systemic treatment. The 8-year DMFI for ultralow-risk patients was 97.0% (95% CI, 95.8 to 98.1), which was 2.5% higher than for patients with low-risk tumors (n = 3,295, 94.5% [95% CI, 93.6 to 95.3]). The hazard ratio for DMFI was 0.65 (95% CI, 0.45 to 0.94) for ultralow versus low risk, after adjusting for clinical-pathologic and treatment characteristics. The 8-year BCSS for ultralow-risk patients was 99.6% (95% CI, 99.1 to 100). Patients with an ultralow-risk 70-gene signature have the best prognosis, distinctive from low risk, with 8-year BCSS above 99%, and very few patients developed distant metastases with an 8-year DMFI rate of 97%. These patients could be candidates for further de-escalation of treatment, to avoid overtreatment and the risk of side effects.

Outcome of patients with an ultralow risk 70-gene signature in the MINDACT trial.

500 Background: Gene signatures have proven successful in identifying patients with a low risk of distant recurrence who could forego chemotherapy (CT) and are currently included in international treatment guidelines for breast cancer. For the 70-gene signature (MammaPrint) an additional threshold was established within the low risk category to identify patients with an ultralow risk of distant recurrence. In independent cohorts, these patients had excellent breast cancer specific survival at 15 years, suggesting that ultralow risk cancers represent indolent disease (Esserman, JAMA Oncol 2017, Delahaye, BC Res Treat 2017). Here we evaluate survival of patients with an ultralow risk 70-gene signature who participated in the randomized phase 3 MINDACT trial (Piccart, Lancet Oncol 2021). Methods: Of the 6,693 patients enrolled in the MINDACT trial (EORTC 10041/BIG 3-04) between 2007-2011, profiling revealed an ultralow risk 70-gene signature in 1,000 patients (15%). We assessed 5- and 8-year distant metastasis free interval (DMFI) and breast cancer specific survival (BCSS) in patients stratified by 70-gene signature result (high, low, ultralow), and within the ultralow risk group stratified by clinical risk. For these exploratory analyses, we used Kaplan-Meier estimates for time to event endpoints and Cox-regression models to calculate hazard ratio’s (HR). Results: Median follow-up was 8.7 years. Among the ultralow risk patients (n = 1,000), 67% were ≥50 years, 81% had tumors &lt; 2cm, 80% were lymph node negative, 96% had grade 1 or 2 tumors and 99% were ER-positive. Systemic therapy was received by 83% of patients (69% endocrine therapy (ET), 14% ET + CT) and 16% received no adjuvant systemic treatment (AST). Survival estimates for all endpoints are shown in the table; 8-year DMFI was 97.0% (95% CI 95.8-98.1) for ultralow risk. The 8-year DMFI in ultralow risk patients who received no AST or ET only was 97.8% (95% CI 95.3-100) and 97.4% (95% CI 96.1-98.7), respectively. The HR for DMFI was 0.66 (95% CI 0.46-0.95) for ultralow vs low risk, after adjusting for tumor and treatment characteristics (preliminary results). Conclusions: In this prospective study, patients with an ultralow risk 70-gene signature have an excellent prognosis with 8-year BCSS above 99% regardless of clinical risk status, and with an 8-year DMFI of 95-98%.[Table: see text]