Clinical Benefit of Adjuvant Capecitabine According To Residual Cancer Burden in Patients With Triple-Negative Breast Cancer With Residual Disease Following Neoadjuvant Chemotherapy.

[BACKGROUND] In early triple-negative breast cancer (TNBC), surgery following neoadjuvant chemotherapy (NAC) is standard. Adjuvant capecitabine has shown survival benefits in patients with residual disease; however, data remain limited regarding the subgroups that benefit most, particularly when stratified by residual cancer burden (RCB), a key prognostic indicator post-NAC.

[METHODS] Patients with early TNBC and residual disease following NAC (Feb 2008-Dec 2021) were retrospectively included. After propensity score matching to balance baseline characteristics, recurrence-free survival (RFS) was compared between patients who received adjuvant capecitabine and those who did not.

[RESULTS] Of 828 eligible patients, 631 were included in the final propensity score matched analysis (222 capecitabine; 409 observation). Median ages were 48 years (range, 40-56) and 50 years (range, 41-56) in the observation and capecitabine groups. RCB distribution was comparable between groups: RCB-I (10% vs. 11%), RCB-II (68% in both), and RCB-III (22% vs. 21%). RCB was prognostic across the cohort, with 3-year RFS rates of 92.2%, 73.6%, and 43.3% for RCB-I, -II, and -III, respectively. Adjuvant capecitabine improved RFS in RCB-III (HR, 0.6; 95% CI, 0.3-0.9; P = .02), but not in RCB-I (HR, 1.1; 95% CI, 0.2-6.5; P = .93) or RCB-II (HR, 0.9; 95% CI, 0.7-1.4; P = .84). In RCB-III, distant metastasis occurred less frequently in the capecitabine group compared with the observation group (34.0% vs. 62.9%).

[CONCLUSION] Adjuvant capecitabine was most beneficial in patients with RCB-III disease, primarily through a reduction in distant metastasis. These findings support its selective use in high-risk TNBC populations.