BACKGROUND EML4-ALK fusion gene, is found in 3 to 5 % of lung adenocarcinoma and can be targeted by tyrosine-kinase inhibitor (TKI) with impressive therapeutic results. METHODS We report the case of a non-smoking 40-year-old woman, diagnosed with metastatic poorly differentiated papillary adenocarcinoma of the lung harbouring the ALK fusion gene. After six cycles of first line chemotherapy with cisplatine-vinorelbine followed by maintenance treatment with erlotinib, the patient achieved a partial response. After disease progression, the patient was included in a trial comparing crizotinib with a classic 2nd line chemotherapy. After 1 month of crizotinib, the patient's condition improved. CT of the chest showed a near-total regression of bilateral pulmonary nodules replaced by pulmonary cysts. CONCLUSIONS We report in this case a dramatic improvement with near-complete vanishing of pulmonary nodules replaced by pulmonary cysts in a patient treated with crizotinib. This case reminds us of the potential importance of evaluating the molecular diagnosis in lung cancers and especially in adenocarcinoma of the lung.