PIK3CA and breast cancer: Since fatty acids (FAs) ranked among the most significantly altered chemical species in breast cancer as compared with normal breast adipose, we then explored FA profiles across tumor tissue stratified by presence of PIK3CA mutation, which occurs in 40% of patients with hormone receptor-positive and human epidermal growth factor receptor 2 negative cancers [13, 14]; and shown to increase tissue arachidonic acid concentrations via PI3K signalling [15].