Objective To find the correlation between phosphatidylinositol kinase-3 catalytic subunit A gene(PIK3CA)mutation and pathological features as well as clinical prognosis of breast cancer.Methods The patho-logical data of 181 patients diagnosed with invasive breast cancer from January 2018 to January 2020 were collected.The estrogen receptor(ER),progestogen receptor(PR),human epidermal growth factor receptor-2(HER2),Ki67 were examined by immuno-histochemistry(IHC).Mutation of exon 9 and exon 20 of PIK3CA were examined by quantitative real-time PCR(qPCR).Results Among 181 cases of invasive breast cancer,70 cases had PIK3CA mutation with 31 cases(44.28%)showed exon 9 mutations and 39 cases(55.71%)showed exon 20 mutations.The difference between PIK3CA mutation and their distribution in molecular typing of breast cancer was statistically significant(P＜0.05).The expression of PIK3CA mutation in breast cancer with different Ki67 expression was sig-nificantly different(P＜0.05).There were 34 cases(48.57%)showed PIK3CA mutations in the HR+/HER2 group and 36 cases(51.43%)of non HR+/HER2 group mutations.There was a statistically significant difference in the distribution of PIK3CA mutations between 2 groups(P＜0.05).The death rate of PIK3CA mutation cases was higher than that of PIK3CA wild type cases(P＜0.05).Conclusions PIK3CA mutation is associated with molecular typ-ing,Ki67 increment index and prognosis of breast cancer.Detection of PIK3CA mutation provides potential support to the development of precise treatment of breast cancer patients.