Abstract
e13058 Background: HER2-low positivity is more prevalent in breast cancers with positive hormone receptor (HR). Patients with HR-positive and low HER2 expression may have different prognosis and characteristics. Nevertheless, research focusing on HR-positive/HER2-low-positive breast cancer remains scarce. Methods: This study included 458 patients with HR-positive/HER2-negative metastatic breast cancer (HR+/HER2- MBC) who received first- or second-line endocrine therapy at the Fudan University Shanghai Cancer Center (FUSCC) between July 2010 and October 2022. Results: Clinicopathological characteristics, HER2 expression in primary and metastatic lesions, treatment patterns, and clinical outcomes of various therapies were compared between the HER2-low-positive and HER2-zero groups. 54.37% (249/458) of the HR+/HER2- MBC patients were HER2-low-positive. Comparable clinicopathological characteristics were observed in the HER2-low-positive and HER2-zero groups. PFS of first- and second-line endocrine treatment was comparable for HER2-low-positive and HER2-zero patients. When taking chemotherapy, the HER2-low-positive group had a shorter PFS than the HER2-zero group (median PFS: 8.64 vs. 9.03 months, p = 0.03). 41.79% (28/67) of HER2-zero primary tumors increased their HER2 score on biopsy, while 41.67% (35/84) of HER2-low-positive tumors became HER2-zero. Patients with an elevated HER2 IHC score from the primary tumor to the metastatic tumor had a longer PFS than those with constant HER2-low-positive status (median PFS: 11.99 months vs. 8.84 months, p = 0.02). Conclusions: HR-positive MBC patients with HER2-low and HER2-zero expression responded similarly to endocrine therapy. But HER2-low-positivity in HR-positive MBC may reduce chemotherapeutic effectiveness and HER2 heterogeneity should be taken into consideration.
Published Version
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