ESR1 and breast cancer: However, our analysis based on publicly available datasets METABRIC, TCGA and TEMPUS showed that 3–9% of the samples classified as ER+/HER2- BC harbour concurrent alterations in both PIK3CA and PTEN (homozygous loss, missense mutations or truncations), in line with a series of data reporting concomitant alterations of the two genes in breast cancer34,35, and in the recent Phase III CAPItello 291 clinical trial8.