Association between the Prevalence of Somatic Mutations in PIK3CA Gene in Tumors and Clinical and Morphological Characteristics of Breast Cancer Patients

The presence of activating somatic mutations in codons 542 and 545 of exon 9 ( p.E542K c.1624G>A and p.E545K c.1633G>A ) and in codon 1047 of exon 20 ( p.H1047R c.3140A>G and p.H1047L c.3140A>T ) of PIK3CA gene encoding catalytic p110α-subunit of phosphatidylinositol-3-kinase was studied in tumors of 473 breast cancer patients by multiplex allele-specific real-time PCR. Fifty-eight (12.3%) different mutations were found. An increase in the frequency of PIK3CA gene mutations with disease progression (from 2.4 to 28.7% with tumor progression from I-IIa to III-IV stage; p =0.0001) and a trend towards its increase in the tumors with unfavorable prognostic characteristics (high histological grade, triple negative phenotype) were demonstrated. The presence of the studied PIK3CA gene mutations in tumors significantly reduces relapse-free survival in the total group and in stage III cancer patients.