Background: Human epidermal growth factor receptor 2 (HER2) is considered a significant driver gene among breast cancer (BC) and a gene locus for anti-HER2 targeted therapy. Amplification of the HER2 gene often indicates poor prognosis. We aimed for evaluation of the impact of low HER2 expression in response to neoadjuvant chemotherapy (NAC) as well as survival outcomes in early luminal BC.

Methods: We conducted this retrospective cohort study on 100 female patients who had early luminal BC with low HER2 expression treated using NAC.

Results: Invasive ductal carcinoma (IDC) was the commonest pathological type (76.0%), and Grade II was the commonest (73.0). T2 was the commonest (78.0%). N2 was the commonest (39.0%), stage II was the commonest (48%), 5-years DFS was (79.7%) with average (30.0±25.52) months while 5-years OS rate was (79%) with the average (38.82±27.54) months, 16% had pathological complete response (pCR) and 84% hadn't pCR with statistically significant difference in distribution.

Conclusion: Our results did not show a significant impact of low HER2 on pCR, DFS, or OS, but showed low pCR achievement especially as most were HR-positive. Low HER2 may be a distinct biological entity that requires further research with a prospective nature and adequate population. With the new HER2 targeting ADCs which prove benefit in low HER-2 patients preparatory activity data, patients with low HER2 may considered a special population subset for finding new treatment options to NAC to improve BC results.