73P Real-world analysis of the use of the 21-gene assay in prognostically intermediate luminal breast cancer (BC): Experience from a French multicenter cohort

Real-world data on indications of Oncotype DX® testing (RS) and its impact on adjuvant chemoendocrine therapy (CET) use in early-stage BC pN0/1 patient (pt) subpopulations and across multiple French centers are limited. We conducted a comprehensive retrospective observational study of BC characteristics, management practices, and therapeutic decision impact of RS results. 952 pts underwent RS testing, including 420 across 2 private clinics (Apr 2014 – Dec 2023), and 505 at Gustave Roussy Institute (Nov 2020 – Dec 2023). Pt characteristics were consistent across private/public centers and were as follows: ≤50y 32.2 %, 51–70y 60.1 %, >70y, 7.7 %; 64.1 % postmenopausal, 35.1 % premenopausal; male 0.8% (n=8). Pathological tumor size, pT1a-b 7.9 %, pT1c 56.2 %, pT2 33.4 %, pT3–4 1.4 %, ypT1c–2, 1.1%; tumor grade 1 13.0 %/ 2 66.6 %/ 3 20.5 %; invasive ductal carcinoma 75.8 %, invasive lobular carcinoma 13.7 %; Ki67 >20%, 49.0 %; pN0 62.7 %, pN1mi 11.4 %, pN1 25.9 %. Retrospective analysis showed that primary reason for testing was for discordant/intermediate histoprognostic factors (73.2 %). Other reasons were the need to confirm endocrine therapy only or CET indication (9.7 %/15.2 %, respectively). Mean test turnaround time was 6.5±2.5 days and was stable over time. As compared to pre-test decisions, RS results led to a 67.6 % reduction in CET use (Table). In pN0 and pN1mi/N1 pts, this reduction was 60.9 % and 78.3 %, respectively. Higher de-escalation rates were observed in pN1mi/N1 pts in most subgroups.Table: 73PIndications of chemoendocrine therapy before/after RS testingCET indicationAll pts≤50y51-70y>70yPre-menopausalPost-menopausalMaleAll pN, n941304564733316028Pre-test (%)89.1 %84.9 %90.8 %93.2 %85.8 %90.7 %100.0 %Post-test (%)28.8 %38.6 %22.5 %37.0 %38.2 %23.9 %12.5 %% decrease-67.6 %-54.5 %-75.2 %-60.3 %-55.5 %-73.6 %-87.5 %pN0, n587230321362483345Pre-test (%)87.1 %83.9 %88.8 %91.7 %85.1 %88.3 %100.0 %Post-test (%)34.0 %42.2 %27.6 %38.9 %41.1 %29.2 %0.0 %% decrease-60.9 %-49.7 %-68.9 %-57.6 %-51.7 %-66.9 %-100.0 %pN1mi/N1, n3497323937822643Pre-test (%)92.6 %87.7 %93.7 %94.6 %87.8 %93.9 %100.0 %Post-test (%)20.1 %27.4 %15.5 %35.1 %29.3 %17.1 %33.3 %% decrease-78.3 %-68.8 %-83.4 %-62.9 %-66.7 %-81.8 %-66.7 % Open table in a new tab RS testing allowed for considerable therapy de-escalation in our cohort, including in specific subpopulations. Our results confirm the test's utility to refine management strategies and avoid overtreatment in daily clinical practice. Cost-effectiveness will be assessed in a pharmacoeconomic substudy.