Docetaxel plus S-1 versus docetaxel plus capecitabine as first-line treatment for advanced breast cancer patients: a prospective randomized phase II study.

Background: This study was conducted to evaluate the efficacy and safety of docetaxel/S-1 (TS) compared with docetaxel/capecitabine (TX) as a first-line treatment for advanced breast cancer.

Methods: Patients with advanced metastatic breast cancer were randomly divided into the TS group (n = 54) and the TX group (n = 57) for first-line chemotherapy from August 2015 to April 2019 (ClinicalTrials.org registration no. NCT02947061). Following the completion of combination therapy, patients without progression received S-1 or capecitabine maintenance treatment. The primary end point was progression-free survival (PFS).

Results: Among 111 enrolled patients, the median PFS did not differ significantly between the TS group and the TX group (TS vs. TX, 9.0 vs. 7.4 months,  = 0.365, 95% confidence interval [CI]: 0.50-1.11, hazard ratio [HR]: 0.75). There was also no statistically significant difference in median overall survival (OS) between the two groups (TS vs. TX, 40.2 vs. 41.3 months,  = 0.976). In addition, visceral metastasis and metastasis sites, such as the liver or lung, did not lead to a significant effect on PFS and OS. The two regimens showed no significant difference in adverse events, except hand-foot syndrome, which predominated in the TX group (38.6% vs. 7.4%,  = 0.001), and diarrhea (24.1% vs. 3.6%,  = 0.003) and elevation of aspartate aminotransferase (AST)/alanine aminotransferase (ALT) levels (14.8% vs. 3.5%,  = 0.049), which were more frequent in the TS group.

Conclusions: The TS and TX regimens demonstrated similar efficacy and safety for the first-line treatment of advanced breast cancer. The TS regimen had fewer cases of severe hand-foot syndrome than the TX regimen, representing an effective alternative option to the TX regimen. Further studies are warranted to define the efficacy and safety of this strategy in real-world settings.