Abstract P4-02-07: Comparison of breast cancer molecular subtyping by Immunohistochemistry and by BluePrint® next generation RNA sequencing-based test at University Hospitals Leuven and Curie Institute Paris

Background MammaPrint® (MP) and BluePrint® (BP) are microarray-based tests with MP being prognostic for distant recurrence and BP enabling stratification into breast cancer molecular subtypes (Luminal, HER2, Basal-type). Recently, a CE marked MP and BP targeted RNA Next Generation Sequencing (NGS)-based kit was developed at Agendia and validated at University Hospitals Leuven and Curie Institute Paris. Here we compare breast cancer molecular subtype stratification defined by immunohistochemistry (IHC) and by MP and BP NGS- and microarray- based tests. Patients and Methods In this study, 124 primary operable invasive breast cancer patients were included at University Hospitals Leuven and at Curie Institute (n=80 Leuven; n=44 Curie) with the following histological subtypes: ductal-NOS (n=100), lobular (n=16), mucinous (n=3), tubular (n=2), others (n=3). Patients with bilateral breast cancer or with >3 positive lymph nodes were excluded. Surrogate breast cancer subtypes based on IHC were defined as follows: luminal if ≥10% estrogen receptor (ER) expression; triple negative if Results Concordance between IHC and MP/BP NGS subtyping was 75.0% (93/124), while concordance between MP/BP on NGS and microarray was 89.5% (111/124). MP/BP NGS subtyping identified more low risk Luminal A tumors compared to IHC (54.0%, (67/124) vs 44.3% (55/124)). Notably, concordance was excellent for triple-negative and, to less extent for HER2 driven tumors (Luminal B-like-HER2 positive and HER2+). IHC vs. MP/BP NGS molecular subtyping (n=124) MP/BP NGSIHCLuminal ALuminal BHER2-positiveBasalTotalLuminal A-like4690055Luminal B-like, HER2-negative16210037Luminal B-like, HER2-positive565016HER2-positive00303Triple negative0101213Total6737812124Microarray vs MP/BP NGS molecular subtyping (n=124) MP/BP NGSMicroarrayLuminal ALuminal BHER2 positiveBasalTotalLuminal A6040064Luminal B7310038HER2-positive028010Basal0001212Total6737812124 Conclusion This study shows a discordance of 25.0% between IHC and BP/MP NGS subtyping. This is in line with previous findings where IHC was compared to molecular subtyping based on microarray (Viale 2017, Whitworth 2014) underlining the complementarity of genomic testing in early stage breast cancer. Moreover, we observed a high concordance between NGS and microarray molecular subtyping, which suggests a successful translation of the MP/BP microarray test to a MP/BP NGS test. Citation Format: Darrigues L, Slembrouck L, Mittempergher L, Delahaye LJ, Vanden Bempt I, Vander Borght S, Vliegen L, Sintubin P, Raynal V, Bohec M, Reyes C, Rapinat A, Helsmoortel C, Jongen L, Hoste G, Neven P, Wildiers H, Smeets A, Nevelsteen I, Punie K, Van Nieuwenhuysen E, Han S, Laurent C, Vincent-Salomon A, Laas-Faron E, Witteveen AT, Neijenhuis S, Glas AM, Floris G, Reyal F. Comparison of breast cancer molecular subtyping by Immunohistochemistry and by BluePrint® next generation RNA sequencing-based test at University Hospitals Leuven and Curie Institute Paris [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-02-07.