278P - Prognostic and biologic significance of HER2-low early-stage breast cancer with long-term follow-up

Background

The advent of trastuzumab deruxtecan has led to the creation of a new treatment criterion for low HER2 expression (HER2-low : HER2 IHC score of 1+ or 2+/ISH not amplified). Utilizing 40 years of detailed clinical data from our hospital, the study aimed to investigate clinicopathological factors and long-term prognosis in HER2-low and HER2-zero breast cancer.

Methods

A total of 4,810 early-stage breast cancer cases were operated on and followed up from 1981 to 2022 at our hospital. We analyzed HER2 expression status in tumor tissues, clinicopathological factors, and prognosis in 3,788 cases excluding stage 0 cases.

Results

HER2-low cases accounted for 48% (1,819/3,788) of all cases analyzed, while HER2-zero cases comprised 34% (1,280/3,788). Among HER2-low cases, 89% were hormone receptor (HR) positive, with 11% classified as triple-negative (TN) breast cancer. In contrast, 83% of HER2-zero cases were HR positive, while 17% exhibited TN. Notably, HER2-zero cases showed a higher proportion of TN compared to HER2-low cases.

Prognostic analysis showed that the HER2-low group exhibited significantly superior outcomes in both disease-free survival (DFS) and overall survival (OS) compared to the HER2-zero group (p=0.005, p

Conclusions

In early-stage breast cancer, HER2-low patients had a better prognosis than HER2-zero patients, suggesting that HER2 expression status may result in different outcomes due to different hormone receptor expression rates and sensitivity to drug therapy.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

T. Toyama: Non-Financial Interests, Personal and Institutional, Invited Speaker: Eli Lilly, Pfizer, Daiichi Sankyo, Chugai, Kyowa Kirin, Eisai; Non-Financial Interests, Personal, Invited Speaker: Taiho, AstraZeneca. All other authors have declared no conflicts of interest.