Activity and Efficacy of Neoadjuvant Chemotherapy in Luminal-HER2 Negative Early Breast Cancer According to HER2 Score (Low vs. Score 0): A Retrospective Study

Background: The predictive and prognostic role of HER2 status in patients with luminal-HER2 negative early breast cancer (BC) undergoing neoadjuvant chemotherapy is unclear. A retrospective analysis evaluating the correlation between HER2 status (low vs. score 0) and pCR/IDFS was conducted. Methods: Patients with BC undergoing neoadjuvant chemotherapy and surgery were included. HER2 low BC was defined as IHC 1+ or 2+ with negative FISH. Logistic regression model and Cox proportional hazard model were adopted to investigate the independent role of HER2 status and outcomes of interest (pCR, CPS-EG and IDFS). Results: About 566 patients were included: 60% were HER2 low and 40% were HER2 0. pCR was achieved in 13.2% of HER2 low versus 17.7% of HER2 0 (P =.15). There was no correlation between baseline HER2 status and CPS-EG score (P =.18). A trend toward improved IDFS for HER2 low BC was observed (P =.07). The relapse rate of the HER2 0 cohort peaked at 12 months after surgery, similar to the HER2 low cohort, which showed an additional peak at 36 months after surgery. Conclusions: Among Luminal-HER2 negative early BCs, our results do not support a clear predictive and prognostic effect of HER2 status, although a trend of worse pCR and better survival for HER2 low BCs cannot be ruled out.