Analysis of databases from transplant recipients revealed a 3-5 fold higher risk to develop de novo malignancies under continued immunosuppression. The underlying mechanisms are poorly understood. Here we describe a patient who received a bilateral lung transplantation for end-stage 'Usual Interstitial Pneumonia' (UIP) resulting in idiopathic lung fibrosis. The recipient presented with a non-small cell lung carcinoma (NSCLC) in the donor lung 7 months later. Molecular and immunological typing of the tumor revealed a cancer of donor origin with a prominent intratumoral immune cell infiltrate without detectable effector function. This is a unique case of de novo outgrowth of a NSCLC of donor origin under continued immunosuppression, supporting the concept of tumor immunosurveillance in vivo.