An Inflammatory myofibroblastic tumor (IMT) is an uncommon, usually benign (non-cancerous) tumor made up of cells called myofibroblastic spindle cells. It usually develops in children or young adults, but can affect people of any age. An IMT can occur in almost any part of the body but is most commonly found in the lung, orbit (eye socket), peritoneum (lining of the abdominal cavity and internal organs), and mesentery. Signs and symptoms vary depending on the site of the tumor. Some people with an IMT are asymptomatic, while others may have nonspecific respiratory symptoms, fever, or pain. IMTs may recur, and become locally invasive and/or spread (metastasize) to other parts of the body. However, malignant (cancerous) IMTs are rare. The underlying cause of IMTs is poorly understood. Some cases have been linked to translocations involving the ALK gene.