218P Characteristics and outcomes of HER2-low (H-Low) and HER2-zero (H-0) advanced breast cancer (ABC) patients (pts) from GEICAM/2014-03 (RegistEM) registry

• DOI: 10.1016/j.esmoop.2023.101407
• Publication Date: 2023-05-15T06:29:52Z
• Authors: I. Alvarez Lopez; A.L. Guerrero Zotano; S. Antolín-Novoa; A. Tibau; C. Falo; M. Hernández Sosa; A. Miguel Rodriguez; A. Rodríguez-Lescure; P. Martinez del P...; J.I. Chacon; M. Corbellas Apar...; J. Cruz Jurado; C.A. Rodríguez Sa...; S. Lopez-Tarruell...; I.G.M. González M...; E. Adrover; A. Blasco Navarro; S. Bezares Montes; F. Rojo

Trastuzumab deruxtecan has shown efficacy in ABC pts with low HER2 positivity by immunohistochemistry (IHC) and a negative situ hybridization (ISH), termed H-Low (HER2 1+, or 2+ ISH). A better understanding of this heterogeneous group is needed. This analysis from RegistEM study (NCT02819882) compares characteristics outcomes H-0 diagnosed Jan-16 to Dec-19. With cut-off 14-Nov-22, an ongoing database, 1232 HER2- were included, 713 519 (IHC1+ 54%, IHC2+ ISH- 46%). Pts split 4 groups based on hormone receptor (HR). HR available tumor sample obtained before the 1st-line (1L). Age, gender, race, menopausal status location (distant metastases unresectable locally advanced disease) similar between at diagnosis. expression (accounting HER2+) was higher de novo metastatic vs early BC pts. Distribution according bone, soft tissue visceral HR+ groups; more reported HR- groups. No. locations regardless status, but 2-3 organs involved observed group. No statistically significant differences PFS OS (even considering IHC1+ & separately), status. Looking primary paired tumors, third changed vice versa, nearly 50% H-0; HER2+ (HR+ HR-) barely changed. Our results show that have than In pts, disease behavior conditioned absence therapies targeted population.