Studies have shown that at least 20–50% of all breast cancer tumours harbour mutations in PI3K (Sanchez et al, 2011; Lopez-Knowles et al, 2014), with mutations of the catalytic subunit of PI3K (PIK3CA) being the most common (Miller et al, 2011; Geuna et al, 2015). This evidence concerns the gene PIK3CA and breast cancer.