['PIK3CA encodes the catalytic subunit of PI3K, p110α. Mutant PIK3CA stimulates the AKT pathway and promotes cancer cell proliferation. PIK3CA mutations have been associated with poor prognosis in patients with colorectal or lung cancer. In contrast, the relationship between PIK3CA mutations and favorable prognoses has been shown in breast cancer. However, the influence of PIK3CA mutations on the prognosis of patients with esophageal squamous cell carcinoma (ESCC) remains unclear.', 'Using a nonbiased database of 219 curatively resected ESCCs and eight esophageal cancer cell lines, we evaluated PIK3CA mutational status by pyrosequencing. The expression of p53 and phosphorylated AKT (i.e., AKT activation) was evaluated by immunohistochemistry.', 'PIK3CA mutations in exon 9 and/or 20 were detected in 46 cases (21%). No ESCC cell line harbored PIK3CA mutations. PIK3CA mutations were significantly associated with phosphorylated AKT expression, but not with p53 expression, sex, age at surgery, tobacco use, alcohol use, or histologic grade. Compared with wild-type PIK3CA cases, patients with PIK3CA mutations in exons 9 and/or 20 experienced significantly better disease-free survival [log-rank P = 0.0089; univariate HR: 0.37, 95% confidence interval (CI): 0.15-0.75, P = 0.0042; multivariate HR: 0.34, 95% CI: 0.10-0.86, P = 0.021] and overall survival (log-rank P = 0.012; univariate HR: 0.38, 95% CI: 0.16-0.78, P = 0.0060; multivariate HR: 0.35, 95% CI: 0.10-0.90, P = 0.028).'] Is pIK3CA mutation associated with a favorable prognosis among patients with curatively resected esophageal squamous cell carcinoma?