[Characteristics of PIK3CA gene mutations in Her2-low breast cancer].

Background: Mutations in the gene, encoding the catalytic subunit of the PI3K class IA p110α, is a common mechanism of activating of PI3K/AKT/mTOR pathway in breast cancer (BC). The detection of these mutations in patients with hormone-positive Her2-negative BC is of important clinical value, since they are the predictor of the sensitivity of the tumor to the PI3K inhibitor - alpelisib. According to the status of the Her2/neu expression, all patients with hormone-positive Her2-negative BC can be divided into two groups - with low expression of Her2/neu (IHC 1+; 2+, ISH-) and with a complete lack of expression of this protein (IHC 0).