Purpose: PIK3CA, encoding for subunit p110a of phosphatidylinositol 3 kinase, is frequently mutated in breast cancer. PIK3CAmutation was predictive for pathological complete response (pCR) in human epidermal growth factor 2 positive breast cancer. This study explores the association of PIK3CA mutation and pCR in triple-negative breast cancer (TNBC) treated with neoadjuvant chemotherapy. Materials and Methods: A total of 92 patients with TNBC derived from a prospectively randomized phase II trial GeparSixto study (NCT01426880). Exon 9 and exon 20 of PIK3CA mutations were evaluated by using classical Sanger method with formalin-fixed paraffin-embedded tumor tissues. Results: Seven of 90 tumors (7.8%) were detectable with a PIK3CA H1047R mutation. Overall, PIK3CA H1047R mutation was significantly associated with a lower pCR rate (14.3% vs. 56.6%; odds ratio, 0.128; 95% confidence interval [CI], 0.015 to 1.108; p=0.047). In carboplatin- containing treatment patients, H1047R mutation trended to predict a lower pCR rate (20% vs. 62.5%; p=0.146). In a multivariable analysis, H1047R mutation trended to predict a lower pCR rate (hazard ratio, 0.1; 95% CI, 0.01 to 1; p=0.056). Conclusion TNBC with a PIK3CA H1047R mutation was less likely to achieve pCR after anthracyclinebased neoadjuvant chemotherapy. Development of H1047R mutant selective inhibitors might be helpful to conquer this subtype of breast cancer.