PURPOSE: Among patients treated with neoadjuvant chemotherapy (NAC), a high survival rate is observed for those who experience a pathological complete response (pCR). Various tumor factors are predictive of a pCR, but few host factors have been studied.We sought to inquire whether or not a patient's blood selenium level prior to treatment was predictive of a pCR. METHODS: We studied 329 women diagnosed with primary invasive breast cancer who were treated with neoadjuvant chemotherapy (NAC). We included patients with HER2-positive ( RESULTS: In the entire cohort, the pCR rate was 59.0% for women in the highest tertileof blood selenium (≥107.19 μg/L) compared to 39.0% for women in the lowest tertile (≤94.29 μg/L) ( CONCLUSIONS: A high selenium level is predictive of pCR in women treated for HER2-positive or triple-negative breast cancer. If confirmed, this observation may lead to a study investigating if selenium supplementation improves pCR rates and survival in breast cancer women receiving NAC.