Inflammatory myofibroblastic tumors (IMT) are a rare tumor, which accounts for 0.04 to 0.1 % of all pulmonary neoplasms. Although IMTs may be benign, they may invade surrounding structures, recur or even metastasize. Here we report a case of a 66-year-old male with locally invasive IMT of the lung with extensive metastases. A 66-year-old male presenting with cough and sputum for three weeks referred to our hospital for evaluation of a mass detected on computed tomography (CT) in the right lower lobe of the lung. CT scan revealed a 4-cm×5.3-cm locally invasive mass and multiple lymph node metastases suspected in both supraclavicular regions, the mediastinal region, and the portacaval region, where positron emission tomography (PET)/CT revealed a high metabolic activity. T2-weighted magnetic resonance imaging (MRI) showed a peripherally enhanced mass-like lesion involving T12 vertebra. Based on radiologic findings, advanced lung cancer with distant metastases suspected. Pathologic examination of the pulmonary lesion demonstrated the proliferation of myofibroblastic spindle cells with lymphoplasmacytic inflammatory infiltration, which suggests the IMT. Excisional biopsy of right supraclavicular lymph node and thoracic vertebra revealed non-specific chronic inflammation with no evidence of malignant cell, which is suspicious of metastases from the pulmonary IMT. All these lesions were negative for rearrangement of anaplastic lymphoma kinase gene immunohistochemically. The patient was treated with a high-dose corticosteroid expecting its anti-inflammatory effect. Interestingly, dramatic improvement of these IMT lesions was demonstrated in the follow-up images on five weeks after the corticosteroid therapy. There was no evidence of disease progression during five months follow-up. Based on our experience, a systemic corticosteroid may be one of the therapeutic options for unresectable IMT with extensive metastases, which has a limited treatment option.