50P - A nationwide retrospective cohort study of the response to neoadjuvant chemotherapy between HER-2 low and HER-2 negative non-metastatic breast cancer in Qatar: A real-world analysis

Background

Breast Cancer is the most diagnosed cancer type worldwide and the second leading cause of cancer-related deaths among women. Anti-HER2 treatment has shifted the treatment paradigm of HER2-positive tumors. Historically, only breast cancer patients with HER2 IHC score of 3+ or with HER2 gene (FISH) amplification have benefited from anti-HER2 agents. However, emerging evidence suggests that even a minimal amplification of HER2 may significantly impact response to therapy and prognosis. This led to the introduction of the new concept of HER2-low breast cancers. Our retrospective analysis aims to unveil the impact of HER2 low expression on the response to neoadjuvant chemotherapy (NACT) in non-metastatic HER2-negative breast cancers.

Methods

All patients’ profiles with non-metastatic, HER2-negative breast cancers who received neo-adjuvant chemotherapy and underwent surgery between the 1^st of January 2018 and the 30^th of August 2022 were retrospectively reviewed. Patients were stratified into HER2-low and HER2-negative groups based on IHC score and FISH amplification. To compare the two study groups, patients’ response was clinically evaluated using surgical pathology reports. The primary endpoint was the response to NACT reported as the objective response rate (ORR) of HER2-low and HER2-negative tumors.

Results

Out of 262 patients, 236 patients had a response. Among the responders, 32 patients (14%) in the HER2-low group had a complete response compared to 4 patients (14%) in the HER2-negative group, OR 0.7 (95% CI:0.2 – 3), p-value= 0.6. While 132 patients (57%) and 17 patients (59%) had a partial response in the HER2-low and HER2-negative groups respectively, OR 0.7 (95% CI:0.2 – 2), p-value= 0.5. Across both groups, more patients with hormone-positive tumors had a response compared to hormone-negative tumors (p-value=0.01).

Conclusions

Preliminary results did not show any statistically significant impact of HER2 low expression on neoadjuvant chemotherapy response. Nonetheless, statistical significance was observed relative to hormone expression, in accordance with the published literature.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Medical Research Center, Hamad Medical Corporation.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.