In line with the observation of recurrent activation of the PI3K pathway in MCC tumours, preclinical and limited clinical data support the efficacy of PI3K–mTOR pathway inhibition in MCC: MCC cell lines are sensitive to inhibition of PI3K and mTOR84,85,176,177, and a complete response to the PI3Kδ inhibitor idelalisib has been reported in one patient, although the response might have been modified by concurrent use of radiotherapy178. The gene discussed is PIK3CA; the disease is neoplasm.