HER2-low, known as HER2 IHC 1+ or 2+ in the absence of a HER2 gene amplification, is an emerging metastatic breast cancer (mBC) subtype in need of more observable data and refined treatment options. Researchers presented their findings at the virtual 2021 ESMO Congress of evaluable prognoses in patients with HER2-low breast cancer based on a national database.

“The ESME mBC platform is a retrospective real-life database using a clinical-trial like methodology to collect data from 18 French Comprehensive Cancer Centers,” explained Jean-Sebastien Frenel, MD, Institut de Cancerologie de l’Ouest René Gauducheau, Saint-Herblain, France, and co-investigators.

The database was designed to maintain data from newly diagnosed mBC patients who received at least one treatment between 2008 and 2016 across all French centers. HER2-low mBC cases were compared alongside to the overall HER2 score 0 population, regarding first-line progression free survival (PFS1), and overall survival (OS).

Out of 15054 HER2 negative mBC patients in the database, 4671 (31%), and 10383 (69%) patients had HER2-low and HER2 0 mBC, respectively. Most of the HER2-low MBC (N=4083, 87.4%) were HR+, with 588 (12.6%) being triple negative.

Metastatic disease was de novo in 37.3% of patients which was significantly higher than HER2 0 mBC patients (27.8%, p<0.0001). The median follow-up time was 49.5 months (48.6-50.4) where the median OS of the HER2-low group was 38 months (36.4-40.5) in comparison to 33.9 months (32.9-34.9) for patients with HER2 0 tumors (p<0.0001).

Findings show that HER2-low patients had a better OS (hazard ratio [HR]=0.95; CI 95% [0.91-0.99], p=0.024) when compared to HER2 0 patients. HER2-low status was not associated with differential PFS1 across the entire population (HR=0.99; CI 95% [0.95-1.02] p=0.45).

“This is the largest study of HER2-low mBC patients to data in a real-world setting. HER2-low mBC may have a distinct outcome from HER2 0 mBC. Dedicated clinical trials are ongoing,” concluded Dr Frenel, et al. – Alexa Stoia