Background: EndoPredict is a prognostic and predictive gene expression assay that provides an EPclin risk score, which can be used to identify individuals with low enough risk of distant breast cancer recurrence that they may forgo chemotherapy. In clinical studies, EndoPredict has been validated to predict risk of distant recurrence up to 15 years and chemotherapy benefit. To date, real-world studies evaluating patient outcomes after prospective EndoPredict testing have been limited. Here, we report on outcomes collected via survey from patients enrolled in a registry created to generate real-world evidence from over 800 patients routinely tested with EndoPredict at Charité University Hospital Berlin. Methods: Female patients with hormone receptor positive, HER2 negative primary breast cancer with up to three positive lymph nodes who received prospective EndoPredict testing at Charité University Hospital Institute of Pathology between 2011 and 2016 were contacted to complete a survey for participation in this study. Surveys included questions on treatment and recurrence history. Patient demographics, clinical characteristics of the cancer, and EndoPredict results were retrieved from Charité records. All patients received EndoPredict test results before decision making on systemic treatment. After testing, treatment included either adjuvant endocrine therapy or adjuvant endocrine therapy plus adjuvant chemotherapy, and may have included radiotherapy. Cox proportional hazards models were fit with binary EPclin risk category (high, low) or continuous EPclin risk score predicting 5-year distant recurrence or recurrence of any kind. Analyses were performed across all survey responses, and in subsets of patients stratified by adjuvant chemotherapy treatment. Kaplan-Meier estimates of 5-year risk of recurrence were also calculated. Results: 842 patient survey responses were returned with informed consent and met study inclusion criteria. The median age at diagnosis was 54 years (IQR 49, 63), and across survey responses, 63.5% (N=535/842) of patients were lymph node negative, 60.9% (N=513/842) were T1, and 43.9% (N=370/842) were treated with adjuvant chemotherapy. Among included patients, 49.5% (N=417/842) were classified as EPclin low-risk and 50.5% (N=425/842) were high-risk. The concordance between EPclin risk category and chemotherapy status was 0.89 with 5.5% (N=23/417) of EPclin low-risk and 81.6% (N=347/425) of EPclin high-risk patients receiving treatment with chemotherapy. In the subset of patients not treated with adjuvant chemotherapy (N=472/842, 55.7%), continuous EPclin score was a significant predictor of distant recurrence (N=469; HR: 4.34, 95% CI 1.75-9.58); p = 2.4 × 10-3), and recurrence of any kind (N=468; HR: 3.39, 95% CI 1.61-6.58); p = 1.9 × 10-3). In EPclin low-risk patients treated with endocrine therapy alone, there was a low risk of 5-year distant recurrence (1.6%, 95% CI 0.7%-3.4%). In EPclin high-risk patients the risk of distant recurrence at 5 years was 6.8% (95% CI 2.6%-17.4%) in patients without chemotherapy and 3.6% (95% CI 2.1%-6.3%) in patients treated with chemotherapy. In an exploratory subgroup analysis in patients with node negative and node positive disease, risk of 5-year distant recurrence in EPclin low-risk patients without chemotherapy was 1.3% (95% CI 0.5%-3.5%) and 2.4% (95% CI 0.6%-9.2%), respectively. Conclusion: In this real-world cohort of patients with prospective routine testing with EndoPredict, EPclin scores were a significant predictor for patient-reported outcomes. Patients with EPclin low-risk scores had a low risk of 5-year distant recurrence even in the absence of chemotherapy treatment. This real-world result supports previous clinical studies demonstrating that patients with EPclin low-risk scores can safely forgo chemotherapy. Citation Format: Wolfgang D. Schmitt, Paul Jank, Inga Hoffmann, Berit M. Pfitzner, Lauren Lenz, Wyatt Clegg, Elke Keil, Sarah Ratzel, Elizabeth S. Cogan, Jens-Uwe Blohmer, Pauline Wimberger, Ralf Kronenwett, David Horst, Carsten Denkert. Retrospective evaluation of outcomes in a real-world, prospective cohort using EndoPredict: Results from the Charité registry [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 P2-03-23.

Aim: The 46-gene Prolaris® cell cycle progression test provides information on the risk of prostate cancer progression. Here we developed and validated a 16-gene kit-based version. Methods: RNA was extracted from prostate cancer biopsy tissue. Amplification efficiency, minimum tumor content, repeatability, reproducibility and equivalence with the 46-gene test were evaluated. Results: Amplification efficiencies for all genes were within the acceptable range (90–110%), and samples with ≥50% tumor content were appropriate for the 16-gene test. Results were repeatable (standard deviation: 0.085) and reproducible (standard deviation: 0.115). Instrument, operator and kit lot had minimal impact on results. Cell cycle progression scores from the 46- and 16-gene tests were highly correlated (r = 0.969; bias = 0.217). Conclusion: The 16-gene test performs consistently and similarly to the 46-gene test.

5030 Background: Most patients would defer using androgen deprivation therapy (ADT) with radiation therapy (RT) when the number-needed-to-treat (NNT) exceeds 25 persons to prevent 1 from developing metastasis, corresponding to an absolute benefit of 4%.1 However, no tools for estimating personalized NNT or absolute benefit from ADT exist. We aimed to quantify personalized absolute benefit and NNT for persons receiving ADT added to single modality RT. Methods: The clinical cell-cycle risk (CCR) score combines the University of California, San Francisco’s Cancer of the Prostate Risk Assessment and the cell cycle progression molecular score to accurately assess prostate cancer aggressiveness. The effect of ADT added to RT was modeled using a 10-year risk of metastasis as a function of continuous CCR score for patients treated with RT alone. The relative benefit of ADT added to RT to reduce distant metastasis was modeled using published data from The Meta-Analysis of Randomized trials in Cancer of the Prostate (MARCAP) which utilized several prospectively randomized RT±ADT trials.2 The average absolute benefit was calculated for patients with CCR scores above and below a prespecified multimodality treatment threshold (MTT) using the distribution of scores in a cohort of patients commercially tested by Myriad Genetics. Results: The commercially tested cohort consisted of 56,485 patients spanning all National Comprehensive Cancer Network risk categories (33.7% very low/low risk, 29.8% favorable intermediate risk, 25.6% unfavorable intermediate risk, 11.0% high/very high risk), with 87.2% having CCR scores at or below the MTT and 12.7% with CCR scores above the threshold. The average absolute benefit of ADT treatment was 0.86% (NNT=116) for patients with CCR scores below the MTT and 8.2% (NNT=12) for patients with CCR scores above the MTT. Patients with CCR scores at precisely the MTT had a predicted absolute benefit of 3.7% (NNT=27). Conclusions: The Prolaris test can accurately predict an individual's benefit of adding ADT to RT, and the risk threshold is consistent with patient attitudes about when to use or omit ADT. 1. Spratt DE, Tward JD: IJROBP 108:899-902, 2020. 2. Kishan AU, Sun Y, Hartman H, et al. Lancet Oncol 23:304-316, 2022.