HER2 expression in primary and recurrent breast cancer samples was highly unstable. Discordance was more frequently observed in the HR-positive population.
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.
Early-stage HR-positive breast carcinomas have low TIL levels regardless of the recurrence risk, molecular subtype, and HER2- low status. These cancers are markedly enriched by HER2-low phenotype, which might have therapeutic implications due to the recently approved anti-HER2 antibody-drug conjugate.