We performed a case:control study including a total of 532 patients (including 266 case:control pairs) with high-risk stage II–III HER2-negative breast cancer to determine whether one or more serum cytokine levels at diagnosis, or 5 years after diagnosis when cancer-free, was associated with distant breast cancer recurrence despite surgery and adjuvant chemotherapy (plus endocrine therapy if ER-positive disease). This evidence concerns the gene ERBB2 and breast cancer.