Identification of E545k mutation in plasma from a PIK3CA wild-type metastatic breast cancer patient by array-based digital polymerase chain reaction: Circulating-free DNA a powerful tool for biomarker testing in advance disease.

PIK3CA gene is frequently mutated in patients with breast cancer and it has been the focus of intense research. Inhibitors of PI3K pathway are being evaluated in ongoing clinical trials but the impact of PIKC3A mutation status on tumor response is yet uncertain. In the metastatic setting, several studies are evaluating the predictive value of PIK3CA mutations. However, results could be biased by biopsy localization. Digital polymerase chain reaction is a new technology that enables detection and quantification of cancer DNA molecules from peripheral blood and can potentially overcome such situation. As a proof of the concept, we present the case of a metastatic patient with a PIK3CA wild-type primary tumor in which the PIK3CA E545K mutation was identified in both the circulating-free DNA obtained from a peripheral blood sample and in the formalin-fixed, paraffin-embedded liver metastasis.