Inflammatory myofibroblastic tumor

Inflammatory myofibroblastic tumor (IMT), also known as inflammatory pseudotumor or plasma cell granuloma, is a rare neoplasm of intermediate biological potential composed of myofibroblastic spindle cells accompanied by an inflammatory infiltrate of plasma cells, lymphocytes, and eosinophils. Although historically considered a reactive or benign process, IMT is now recognized as a true neoplasm that can recur locally and, in rare cases, metastasize. It most commonly arises in the lungs, abdomen (mesentery, omentum, retroperitoneum), and pelvis, but can occur in virtually any anatomical site including the liver, bladder, spleen, and soft tissues. IMT affects children and young adults most frequently, though it can occur at any age. Key symptoms depend on the tumor's location and size and may include a palpable mass, abdominal or chest pain, fever, weight loss, fatigue, and laboratory abnormalities such as anemia, elevated erythrocyte sedimentation rate (ESR), elevated C-reactive protein (CRP), thrombocytosis, and hypergammaglobulinemia. Constitutional symptoms are thought to result from cytokine production, particularly interleukin-6, by the tumor cells. Approximately 50% of IMTs harbor rearrangements involving the ALK (anaplastic lymphoma kinase) gene on chromosome 2p23, and other kinase fusions (involving ROS1, PDGFRB, RET, and NTRK3) have also been identified. Complete surgical resection remains the primary treatment and is often curative. For unresectable, recurrent, or metastatic disease, targeted therapies such as ALK inhibitors (e.g., crizotinib) have shown significant clinical benefit in ALK-positive tumors. Corticosteroids, nonsteroidal anti-inflammatory drugs, and chemotherapy have been used with variable success in cases not amenable to surgery or targeted therapy. Prognosis is generally favorable, with local recurrence rates reported between 15–25% after incomplete resection.

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