Purpose: In a prespecified GEICAM_CIBOMA trial (NCT00130533) correlative analysis, PAM50 non–basal-like breast cancer (non- BLBC) status distinguished patients with triple-negative breast cancer (TNBC) who are most likely to benefit from adjuvant capecitabine. The standardized forkhead box C1 (FOXC1) IHC test has demonstrated strong reliability in classifying the BLBC subtype throughout TNBC cohorts. This translational analysis aimed to evaluate the prognostic/predictive significance of BLBC classification by FOXC1 IHC in the phase III GEICAM_CIBOMA clinical trial. Experimental Design: Tumor tissues from patients with TNBC randomized to standard (neo)adjuvant chemotherapy followed by capecitabine versus observation were analyzed using the standardized FOXC1 IHC test to assess its BLBC/non-BLBC TNBC subtyping capacity as a distant relapse-free survival clinical outcome predictor of cape...