High CAP1 tumor expression was associated with shorter overall survival (adjusted hazard ratio [HRadj] 1.54; 95% confidence interval [CI], 1.11–2.13) and relapse-free survival (HRadj 1.47; 95% CI, 1.10–1.96), compared with low or intermediate CAP1 expression, particularly among ER-positive tumors or lymph node positive tumors. Here, ESR1 is linked to neoplasm.