This is a prospective study assessing efficacy of trastuzumab therapy in pretreated NSCLC patients. Patients with locally advanced or metastatic NSCLC, HER2 FISH positive and/or with HER2 gene mutation, pretreated with at least one previous chemotherapy line will be considered eligible for the trial. After evaluation of inclusion and exclusion criteria, and after signature of informed consensus form, all eligible patients will receive trastuzumab 6 mg/kg every 3 weeks (8 mg/kg loading dose) until disease progression, unacceptable toxicity or patient refusal.