Effect of capecitabine as monotherapy for HER2 normal metastatic breast cancer

This study aimed to evaluate the efficacy of capecitabine monotherapy for patients with human epidermal growth factor receptor-2 (HER2) normal metastatic breast cancer (MBC). The primary endpoint was progression-free survival (PFS), and secondary endpoints included overall survival (OS) and PFS according to treatment line and estrogen receptor (ER) status. Patients who received capecitabine as monotherapy for HER2 normal MBC from 2010 to 2020 were included in this retrospective study. ER status, treatment line, number of treatments, and dates of progression and death were registered. PFS was defined from capecitabine initiation to progression or any cause of death, and OS until any cause of death. Among 162 patients receiving capecitabine, approx. 70% had ER-positive disease. They received a median of six cycles of capecitabine (range 2-45). The median PFS was 4.3 months, with no significant difference between treatment lines. When analyzing PFS according to ER status, a statistically significant difference was observed between those with ER-positive and ER-negative disease, with a median PFS of 5,3 months versus 2,5 months, respectively (p = 0.006). A similar trend was seen for overall survival, with a median OS of 14 months for all patients and 17.8 months versus 7.6 months for patients with ER-positive and ER-negative disease, respectively (p ≤ 0.0001). Patients with HER2 normal MBC receiving monotherapy capecitabine had a median PFS of 4.3 months, and a median OS of 14 months. PFS was consistent regardless of treatment line but differed significantly according to ER status.