Evolution and prognostic significance of HER-2 conversion from primary to residual disease in HER-2 negative patients with breast cancer after neoadjuvant chemotherapy.

This study aimed to analyze HER-2 zero or HER-2 low conversion in HER-2 negative patients after neoadjuvant chemotherapy (NAC) and evaluate its prognostic significance. HER-2 negative patients with breast cancer with residual disease after NAC and paired pre- and post-therapeutic HER-2 testing results were analyzed retrospectively. HER-2 low, defined as immunohistochemistry (IHC) scores of 1+ or 2+/in situ hybridization (ISH), were not amplified. HER-2 zero is defined as an IHC score of 0. A total of 571 patients were enrolled, including primary HER-2 zero (n=201, 35.2%) and HER-2 low (n=370, 64.8%). The overall HER-2 change rate was 32.4%. Multivariable logistic regression showed that patients with hormone receptor-positive status before NAC was significantly associated with the conversion of HER-2 zero to low (OR=3.436, < 0.0001). The median follow-up time was 50.0 months. In patients who are primary HER-2 zero, HER-2 zero to low was significantly associated with better disease-free survival (DFS) than constant HER-2 zero (HR=0.49, =0.01) after adjustment (4-year DFS 80.1% vs 55.7%, Log-rank =0.033). Subgroup analysis revealed that among patients who are primary HER-2 zero with hormone receptor-positive, HER-2 zero to low had a significantly better DFS than constant HER-2 zero (Log-rank =0.037). In contrast, patients with hormone receptor-negative status did not. In conclusion, almost one-third of patients who are HER-2 negative underwent HER-2 zero or HER-2 low conversion after NAC. HER-2 zero to low conversion was associated with better DFS in patients who are HER-2 zero. These results provide a valuable reference for the potential application of anti-HER-2 ADC in an adjuvant setting for patients with residual disease after NAC.