Abstract P1-07-09: Clinical and pathologic characteristics in early breast cancer Her2-low and high risk Oncotype DX RS
Authors: Galve Elena , Pikabea-Diaz Fernando , Lopez-de-San-Vicente-Hernandez Borja , Figaredo-Berjano Covadonga , Legaspi-Folgueira Jairo , Sala-Gonzalez Maria Angeles , Arango-Arteaga Juan Fernando , Fernandez-Ferrer Sara , Loaiza-Jaramillo Pablo Leonardo , Casado-Cuesta Pablo , Temino-Frances Marina , Bilbao-Penas Anne , Martinez-del-Prado Purificacion 
Published: March 2023

Abstract
Background: Recent data suggest that HER2-low breast cancer (BC) may represent a distinct entity. Approximately 55-60% of BC are considered as Her2-low, of which 80% are Luminal-like tumors. Recent studies support potential clinic-pathological and molecular features differences between Estrogen Receptor (ER) positive HER2-low and ER positive Her2-0 disease. Among patients (pts) with high genomic risk (Oncotype DX RS) HER2-low expression was associated with a significant improvement in overall survival compared to Her2-0. The objective of our study is to compare disease characteristics and outcomes between HER2-low and Her2-0 in estrogen receptor (ER) positive, early (e) BC. (Murtai R et al. The Breast. 60(2021)62-69.
Methods: A single center retrospective study of all pts. with ER positive, Her2 negative eBC, for whom Oncotype DX test was performed between 1/Nov/2012 and 14/Febr/2019. The pts were separated into HER2-low (immunohistochemistry (IHC) +1 or + 2 and in situ hybridization not amplified) or HER2-0. Clinic-pathological features included were: demographics, tumour size, nodal status, histologic grade, Her2 expression, ER and progesterone receptor (PR), Ki-67, presence of lymph-vascular (LV1) tumor cell invasion and Oncotype recurrence score (RS) result.
Results: A total of 344 pts were screened, of whom 297 pts were included (Exclusion for: Her2 “negative” expression (45 pts); HER2 positive disease by IHC (1 pts); metastatic disease (1 pts)). The distribution of HER2-0 and HER2-low subgroups was 121 pts (41%) and 176 pts (59%). The pathological characteristics according to Her2 expression status are summarized in Table 1. Median age was 57 year (38-79), similar between both groups: Her2-0 58 yr (41-78) and 56 yr (38-79) in Her2 low. The postmenopausal status was 76 pts (62,8%) Her2-0 Vs 113 pts (64,2%) in Her2 low. 1 pts was male. Proliferation Index: Ki67% &lt; 20 was: 65 pts (53,7%) Her2-0 Vs 86 pts (48,5%) in Her2 low; 65 pts (13,5%) had Lympho-vascular invasion in Her2 low; 115 pts (95%) were ER positive in Her2-0 Vs 157 pts (89,2%) in Her2 low; PR positive &gt; 20 was 106 pts (87,6%) in Her2-0 Vs 137 (78,7%) in Her2 Low. The median follow-up was 72 month (SD+- 22,52). 5 pts had a recurrence: 4 pts were Her2 low (1 local and 3 distant metastasis) and 1 Her2-0 with distant metastasis. Most of the pts received adjuvant hormone therapy. There were no statistically significant differences between both groups owing to neither the clinic-pathologic features nor the recurrence score. It was not reached the mínimum number of events for a survival analysis.
Conclusions: Our results show that HER2-low eBC pts have similar characteristics and survival rates compared to HER2-0 BC pts without significant differences.
Table 1. Baseline pathological characteristics.
Citation Format: Elena Galve, Fernando Pikabea-Diaz, Borja Lopez-de-San-Vicente-Hernandez, Covadonga Figaredo-Berjano, Jairo Legaspi-Folgueira, Maria Angeles Sala-Gonzalez, Juan Fernando Arango-Arteaga, Sara Fernandez-Ferrer, Pablo Leonardo Loaiza-Jaramillo, Pablo Casado-Cuesta, Marina Temino-Frances, Anne Bilbao-Penas, Purificacion Martinez-del-Prado. Clinical and pathologic characteristics in early breast cancer Her2-low and high risk Oncotype DX RS [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 P1-07-09.