['The phosphatidylinositol-3-kinase (PI3K)-AKT signaling pathway is considered to play an important role in tumorigenesis. Frequent somatic mutations in the PI3K subunit p110a (PIK3CA) occur in a variety of cancer types. The purpose of this study was to determine the relationship between PIK3CA mutation in breast cancer and pathological features and outcome of patients.', 'The PIK3CA mutations in exons 7, 9, 20 were screened in 250 primary breast cancers using PCR and fluorescent (F)-SSCP, and the results were analyzed according to their cliniopathological data.', 'The frequency of PIK3CA mutations among the 250 cases was 35.2% (88/250), point mutations in exon 7 were found in 8 (3.2%) cases,40 (16.0%) cases in exon 9 and 47 (18.8%) cases in exon 20. No significant correlation between PIK3CA mutation and age, histological type, differentiation, and lymph node metastasis was observed. Mutations were associated with larger tumor size (P = 0.004) and positive estrogen receptor status (P = 0.008). Patients with PIK3CA mutations showed a significantly worse survival (P = 0.004), particularly in those with positive estrogen receptor expression or non-amplified HER-2 (both P = 0.002).'] Is [ PIK3CA mutation an independent indicator of malignant phenotype and prognosis in breast cancer ]?