Finally, a patient with ovarian cancer and a PIK3CA H1047R mutation in an original FFPE tumor sample, who had dramatic but short-lived response to an investigational agent targeting PI3K alpha, was found, in addition to having a PIK3CA H1047R mutation (0.08%), a low frequency KRAS G12C mutation (0.03%) in cfDNA from plasma collected before initiation of a PI3K inhibitor, which can reasonably explain early therapeutic failure. The gene discussed is PIK3CA; the disease is ovarian cancer.