Abstract: Objective The inflammatory myofibroblastic tumor （IMT） is a mesenchymal tumor with infiltrating and worsening characteristics，usually in the lungs. Because IMT lacks specific clinical symptoms and the imaging findings are changeable，it is easy to be misdiagnosed. This article discusses the pathogenesis，clinical manifestations，diagnosis，treatment，and prognosis of IMT and provides clinical experience for improving the accuracy of diagnosing mesenchymal tumors. Methods The imaging manifestations of a case of breast ductal carcinoma in situ combined with pneumonia myofibroblastoma confirmed by surgery and pathology were analyzed retrospectively. A review and review of the relevant literature on the pathogenesis， clinical features， imaging manifestations， treatment methods， and prognosis of IMT was summarized. Results Pneumonia myofibroblastoma was clinically dyspnea or fever，cough，sputum，chest tightness，etc. Laboratory tests were not specific and may have reduced hemoglobin concentration，increased thrombocytosis，and increased sedimentation rate. It was divided into infiltrating type，mass type，and nodular type on the image. The mass type was more common，mostly single，round，or quasi-circular，and mostly in the superficial part of the lung. Pathology was the gold standard for IMT diagnosis. The tumor was composed of differentiated myofibroblastic spindle cells，arranged in bundles or spirals， with a large number of plasma cells and/or lymphocytes infiltration in the interstitium. Immunohistochemistry showed the spindle shape cells expressing smooth muscle actin and vimentin with a good prognosis，and surgical resection was the main treatment. Conclusion The clinical manifestations of IMT are not specific. The diagnosis is based on a chest X-ray，chest CT，and percutaneous lung biopsy. The only way to confirm IMT is through pathological examination. The microscopic findings are woven-like spindle cells with many inflammatory cells. Surgical resection is the primary treatment method，and the prognosis depends on the quality of surgical resection and the tumor size.

Key words: breast cancer, lung metastasis, pneumonia myofibroblastoma