Abstract 1030: Concordance between the DESTINY-Breast04 clinical trial assay (4B5[CDx]) and other HER2 IHC assays for HER2-low breast cancer in real-world practice: First phase of a large-scale, multicenter global ring study
Authors: Schildhaus Hans-Ulrich , Badve Sunil , D’Arrigo Corrado , Farshid Gelareh , Lebeau Annette , Peg Vicente , Penault-Llorca Fréderique , Rueschoff Josef , Yang Wentao , Atkey Neil , Baumann Jessica , Beyerlein Elisabeth , Newell Amy Hanlon , Penner Alexander , Moh Akira , Viale Guiseppe 
Published: March 2024

Background: DESTINY-Breast04 (DB-04) showed that trastuzumab deruxtecan improves survival vs chemotherapy in patients with human epidermal growth factor receptor 2 (HER2)-low (immunohistochemistry [IHC] 1+ or IHC 2+ with in situ hybridization negative) metastatic breast cancer (BC). The VENTANA 4B5(CDx) IHC assay, now approved in the United States (US) as a companion diagnostic, was used as the clinical trial assay (CTA) in DB-04. Real-world differentiation of HER2-low vs HER2 IHC 0 BC with non-CTAs is difficult. This is the first phase of a study assessing agreement between CTA and non-CTA scores.

Methods: 50 clinical BC samples with HER2 IHC scores of 0, 1+, 2+, and 3+ were sent to laboratories in Europe, Canada, and the US for HER2 IHC testing per ASCO/CAP 2018 guidelines. After routine protocol scoring, pathologists were trained and rescored the samples 2 weeks later. Post training scores were compared with reference CTA scores determined by a central laboratory and a panel of experts. The primary endpoint was positive percentage agreement (PPA) and negative percentage agreement (NPA) between CTA and non-CTA scores, assessed after training, considering HER2-low as positive and HER2 IHC 0 as negative.

Results: A total of 3449 post training non-CTA scores were available for analysis. PPA for HER2-low vs HER2 IHC 0 was 87.5% and NPA was 61.9%, with Cohen κ of 0.51 (Table). HER2-low vs HER2 IHC 0 agreement between CTA and non-CTA varied across subgroups. PPA &gt;95% was shown with 4B5 Laboratory Developed Tests (LDTs) and HercepTest (Omnis), NPA of 80% with Leica, and overall agreement &gt;80% with HercepTest (Link48), 4B5 LDTs, and German, French, and Italian laboratories.

Conclusions: The degree of concordance between the CTA and non-CTAs varied among assay types and laboratory locations. A low NPA for some non-CTAs suggests the need for further assay optimization for HER2 IHC 0 evaluation.

Post training non-CTA results HER2-low vs HER2 IHC 0 BC Post training scores PPA (95% CI), % NPA (95% CI), % Overall percentage agreement (95% CI), % Cohen κ (95% CI) Overall non-CTA test results (N = 3449) 87.5 (86.0-89.0) 61.9 (58.9-64.9) 78.7 (77.1-80.1) 0.51 (0.48-0.54) Non-CTA subgroups HercepTest (Omnis) (n = 467) 95.5 (92.3-97.7) 36.9 (28.9-45.4) 75.2 (70.8-79.4) 0.37 (0.28-0.46) HercepTest (Link48) (n = 790) 88.5 (85.2-91.2) 64.3 (57.8-70.4) 80.3 (77.2-83.2) 0.55 (0.48-0.61) Leica (n = 96) 59.3 (45.0-72.4) 80.0 (61.4-92.3) 66.7 (55.5-76.6) 0.35 (0.17-0.53) Non-4B5 LDTs (n = 1609) 83.8 (81.2-86.1) 67.8 (63.5-72.0) 78.2 (75.9-80.3) 0.52 (0.47-0.57) 4B5 LDTs (n = 487) 96.0 (93.0-98.0) 58.8 (50.4-66.8) 83.0 (79.1-86.4) 0.59 (0.51-0.68) Country subgroups Germany (n = 340) 93.1 (88.5-96.3) 64.4 (54.2-73.6) 83.1 (78.3-87.2) 0.61 (0.51-0.70) France (n = 342) 95.4 (91.5-97.9) 64.4 (54.4-73.6) 84.7 (80.1-88.6) 0.64 (0.55-0.73) Italy (n = 395) 89.9 (85.2-93.5) 72.5 (63.6-80.3) 83.9 (79.6-87.6) 0.64 (0.55-0.72) Spain (n = 567) 83.0 (78.4-86.9) 64.2 (56.6-71.3) 76.3 (72.3-80.0) 0.48 (0.40-0.56) US/Canada (n = 1029) 86.6 (83.6-89.2) 61.8 (56.1-67.3) 78.2 (75.4-80.8) 0.50 (0.44-0.56) Europe, other (n = 776) 85.0 (81.3-88.2) 52.8 (46.2-59.3) 73.8 (70.3-77.1) 0.40 (0.32-0.47)

Citation Format: Hans-Ulrich Schildhaus, Sunil Badve, Corrado D’Arrigo, Gelareh Farshid, Annette Lebeau, Vicente Peg, Fréderique Penault-Llorca, Josef Rueschoff, Wentao Yang, Neil Atkey, Jessica Baumann, Elisabeth Beyerlein, Amy Hanlon Newell, Alexander Penner, Akira Moh, Guiseppe Viale. Concordance between the DESTINY-Breast04 clinical trial assay (4B5[CDx]) and other HER2 IHC assays for HER2-low breast cancer in real-world practice: First phase of a large-scale, multicenter global ring study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1030.