Abstract: Background and purpose: Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal malignancy which occurs primarily in children and adolescents. Complete surgical resection is the major treatment, and conventional chemotherapy and radiotherapy are usually invalid. In this study, we retrospectively analyzed the clinical and pathological features of eleven patients with adult IMT. Methods: A total of eleven patients with adult IMT were enrolled into this study between Feb. 2013 and Nov. 2017 in Fudan University Shanghai Cancer Center. The clinical and pathological data, treatment and prognosis were analyzed. Results: Among the eleven patients with adult IMT, five patients were male (45%), six patients were female (55%), and the median age was 39 years (24-74 years). The primary tumor located in the lung was found in two patients (18%), two cases (18%) in the retroperitoneum, and seven cases (64%) in the abdominopelvic region. Four cases were abdominal epithelioid inflammatory myofibroblastic sarcoma (EIMS). The positive rate of anaplastic lymphoma kinase (ALK) immunohistochemical expression was 82% (9/11), and the positive rate of ALK translocation was 86% (6/7). Seven patients with ALK-positive advanced disease received the treatment of crizotinib, the response rate was 86%, and the median progression-free survival (PFS) was 20.8 months (95% CI: 7.6 months-34.0 months). Conclusion: The treatment of crizotinib in adult patients with ALK-positive advanced IMT and EIMS resulted in very high response rate and long-term PFS, which suggested that ALK signaling pathway may play an important role in the development of adult IMT. It deserves further investigation.

Key words: Inflammatory myofibroblastic tumor, Epithelioid inflammatory myofibroblastic sarcoma, Anaplastic lymphoma kinase, Crizotinib