A number of factors may explain why arachidonic acid did not appear significantly elevated in our PIK3CA mutant tissues including the broad range of heterogenous tumor cell content of our samples (30-100%) and the fact that tissue pools of arachidonic acid can also arise from delta-6-desaturation of linoleic acid (FA(18:2)) which is generally enhanced in breast cancer tissue but especially in estrogen receptor-negative samples [28]. The gene discussed is ESR1; the disease is breast cancer.