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. Treatment involves surgical removal when possible, although there are reports of treatment with oral steroids and radiation therapy.

The underlying cause of inflammatory myofibroblastic tumors (IMTs) remains unknown. While some researchers believe it is a true neoplasm, others believe that it represents an immunologic response to an infectious or noninfectious agent. Several associations have been reported between IMT and infections, including:

• organizing pneumonia
• Mycobacterium avium intracellulare
• Corynebacterium equi (a bacteria that affects the lungs)
• Campylobacter jejuni (a common cause of gastroenteritis)
• Bacillus sphaericus
• Coxiella burnetii
• Epstein-Barr virus
• E. coli
• occlusive phlebitis of intrahepatic veins

Associations have also been reported between IMT and:

• previous abdominal surgery
• trauma
• ventriculoperitoneal shunt
• radiation therapy
• steroid usage

An inflammatory reaction to an underlying, low-grade malignancy has also been proposed as a cause. Because there is limited information available to support or refute any of these, the mechanism behind the development of IMTs is still unclear.

In general, inflammatory myofibroblastic tumors (IMTs) follow a benign course with a favorable outcome after they are surgically removed. In some cases, they can be invasive, recur locally, or spread (metastasize). A metastatic IMT has a poorer prognosis and can cause death. An IMT can also be indolent, with prolonged survival despite multiple recurrences. Local recurrence rates of 15% to 37%, and distant metastasis rates of up to 11%, have been reported. Rearrangements of genetic material involving the ALK gene are present in the tumor in some affected people (known as being ALK-positive). Being ALK-positive may be associated with a more favorable prognosis. One study found that a higher percentage of patients with localized disease were ALK-positive (about 60%) compared to those with multicentric (having 2 or more separate growths) IMTs (about 33%). However, the associations between prognosis and ALK status need to be validated with additional, larger studies.