Breast Cancers with a HER2/CEP17 Ratio of 2.0 or Greater and an Average HER2 Copy Number of Less Than 4.0 per Cell: Frequency, Characteristics and Survival Outcomes in those Receiving HER2-targeted Treatment

Abstract

Purpose: 2018 ASCO CAP testing guidelines for HER2 recommended a change from ‘positive’ to ‘negative’ in cases of IHC 2+, FISH HER2/CEP17 ratio ≥2.0 and HER2 copy number <4 – known as ‘group 2’ cases [1,2]. In the UK, these cases are positive, but borderline amplified with uncertain benefit of anti-HER2 treatment [3]. Ahead of a forthcoming review of HER2 testing guidelines by the UK National Coordinating Committee for Breast Pathology, we aimed to identify real-world data on group 2 patients, including frequency, characteristics and outcomes in those treated with anti-HER2.