Treatment and prognosis of advanced triple-negative breast cancer patients with HER2-low expression: A 15-year retrospective study.

e13046 Background: There is some tumor defined HER2 1+ or 2+ by IHC and negative in FISH as HER2 low expression in common triple-negative breast cancer (TNBC). This subset is considered to be a new subtype of HER2-low BC, which might benefit from HER2-targeted antibody drug conjugate (ADC). Therefore, it could preliminarily understand on treatment status and treatment needs of HER2-low BC by analysis of the distribution, treatment patterns and prognosis of HER2-low BC in advanced TNBC. Methods: This was a retrospective study which included HR-negative, HER2 IHC 0/1+/2+ and FISH negative ABC patients (pts) diagnosed from June 2006 to September 2020, with recurrence and de novo metastatic cancer at a single institution in China. The cut-off date of follow-up was 31 December 2020. The baseline characteristics, first- and second-line therapies and the clinical outcomes were reported. Results: In total of 195 pts with complete follow-up data were included into final analysis. HR-negative, HER2 IHC 0 pts (triple negative, TN pts) were 61.5% (n = 120), and HR- negative, HER2 IHC 1 + / 2 + and FISH negative pts (HER2-low pts) were 38.5% (n = 75). The baseline characteristics and treatment patterns of HER2-low pts and TN pts were similar. The median age of pts at diagnosis was 48 years old while 54.4% pts were premenopausal. About 80% pts were recurrence, and 27.6% of them received neoadjuvant chemotherapy. The median disease-free interval (DFI) in early stage was 15.5 months, with 66.0% pts for DFI≥12 months. 56.4% of the pts presented with visceral metastasis. The most common sites of metastasis were lung (35.4%), lymph node (27.7%), soft tissue (24.1%), liver (20.5%), bone (20.5%), and brain (6.2%). The most commonly used regimens for first- and second-line were combination chemotherapy, which were 74.7% and 65.3%, respectively; paclitaxel (55.6%) and platinum (43.8%) were the most commonly used drugs for the first-line treatment. Only 14.4% and 3.6% pts received targeted combination therapy and immunotherapy in advanced setting, respectively. In TN and HER2-low ABC pts, the median PFS of first-line treatment were both 7.2 months, and the median OS was 17.2 months and 17.0 months, respectively. In DFI≥12 months and DFI<12 months subgroup, the median PFS was 8.4 months vs. 4.7 months, with a median OS of 17.8 months vs. 14.4 months, respectively. No significant different was observed between HER2-low pts and TN pts. Conclusions: Based on this observational cohort study, there is no significant difference in the current treatment patterns and prognosis between HER2-low pts and TN pts. However, with the emergence of HER2-targeted ADC therapy, HER2-low ABC pts which were commonly defined as TNBC may benefit from these novel therapies. The recurrence subgroup with DFI≥12 months presented a trend of longer OS, suggesting the therapy mode and response in early stage should be considered in advanced TNBC treatment.