Inflammatory myofibroblastic tumor is a rare growth that develops when specialized cells called myofibroblasts multiply abnormally, often creating a confusing picture for doctors because it can look like many other conditions—and while it’s generally not aggressive, it sometimes comes back or spreads to nearby areas.

What Is Inflammatory Myofibroblastic Tumor?

Inflammatory myofibroblastic tumor, often shortened to IMT, is an uncommon type of growth that forms from cells called myofibroblasts. These are specialized cells that normally help maintain the structure of organs and assist in wound healing. When they grow out of control, they form a tumor that is usually surrounded by many immune cells, which makes the growth look inflamed or infected under the microscope. This confusing appearance is why doctors sometimes mistook these tumors for infections or other conditions in the past.^[1]

IMT is classified as a tumor with limited potential to spread. This means that while it is not typically considered a full cancer, it can invade nearby tissues and sometimes recur after treatment. Distant spread to other organs is very rare, occurring in approximately 5% of cases.^[2] The tumor usually appears as a single mass and can develop in many different parts of the body, though certain locations are more common than others.^[1]

This condition was previously known by many different names, including inflammatory pseudotumor, plasma cell granuloma, and inflammatory fibrosarcoma. These various terms reflected confusion about whether IMT was a reaction to inflammation or a true tumor. Modern understanding recognizes it as a distinct tumor type, and the World Health Organization reclassified it in 2020 as a specific form of intermediate fibroblastic tumor.^[2]

How Common Is Inflammatory Myofibroblastic Tumor?

IMT is an extremely rare condition. In the United States, only about 150 to 200 new cases are diagnosed each year, making it affect less than one in one million people.^[2][12] Because of this rarity, many doctors may never encounter a case throughout their entire careers, which can make diagnosis challenging.

The tumor can occur at any age, but it predominantly affects children and young adults. Some studies have shown that the average age at diagnosis is around 9 years in children, though adults can also develop IMT.^[11] There does not appear to be a significant difference in occurrence between males and females, meaning both sexes are equally likely to develop this condition.^[9]

IMT can develop in virtually any part of the body. However, certain locations are more frequently affected. The most common sites include the lungs, abdominal cavity, and retroperitoneum (the space behind the abdominal organs).^[1] When IMT occurs in the lungs, it represents one of the most frequent types of lung tumors seen in children, accounting for between 16% and 38% of pediatric lung tumors in various studies.^[10]

What Causes Inflammatory Myofibroblastic Tumor?

The exact cause of inflammatory myofibroblastic tumor remains unclear, though scientists have made significant progress in understanding what happens inside the cells when this tumor forms. Unlike infectious diseases that can be traced to specific germs, IMT appears to develop when certain genetic changes occur within cells.

The most important discovery about IMT is that many cases involve chromosomes breaking apart and rejoining incorrectly. Chromosomes are structures inside cells that contain all genetic information. When pieces of different chromosomes fuse together abnormally, they can create what are called fusion genes, which produce abnormal proteins that drive tumor growth.^[12]

In approximately 50% to 80% of IMT cases, there is a rearrangement involving the ALK gene (anaplastic lymphoma kinase). This gene normally helps control cell growth, but when it fuses with other genes, it creates a protein that signals cells to grow uncontrollably.^[5][8] Other genetic abnormalities have been found in IMT as well, including fusions involving ROS1, NTRK3, RET, and PDGFRB genes, though these are less common.^[10]

Some researchers have suggested possible connections between IMT and prior infections, as well as certain immune system conditions. Cases have been reported in association with bacterial or viral infections, and in people with conditions like Sjogren syndrome or after organ transplantation.^[15] However, these associations are not consistent enough to establish clear causal relationships, and the exact triggers remain unknown.

Who Is at Risk for Inflammatory Myofibroblastic Tumor?

Because the underlying cause of IMT is not fully understood, identifying specific risk factors has proven difficult. The condition appears to develop randomly, without clear patterns that would suggest preventable risk factors.

Age is perhaps the most notable demographic factor. Children and young adults are more likely to develop IMT compared to other age groups, though the tumor can occur at any age. Some research suggests that younger patients may have different outcomes, with age being considered a prognostic factor in some studies.^[8]

The location where the tumor develops may influence how it behaves. Studies have found that IMT occurring in the abdominal cavity tends to have higher recurrence rates compared to tumors in other locations. Larger tumors, particularly those exceeding 8 centimeters in size, have also been associated with higher chances of recurrence.^[8] However, these are characteristics of the tumor itself rather than risk factors for developing IMT in the first place.

There is no evidence that IMT is more common in any particular ethnic or racial group, nor does it show preference for one geographic region over another. Similarly, lifestyle factors such as diet, exercise, smoking, or alcohol consumption have not been linked to increased risk of developing IMT.

What Are the Symptoms of Inflammatory Myofibroblastic Tumor?

The symptoms of inflammatory myofibroblastic tumor vary greatly depending on where the tumor grows and how large it becomes. Many people with IMT do not experience any symptoms at all, and their tumors are discovered incidentally during routine health checkups or imaging tests performed for other reasons.^[3][15]

When symptoms do occur, they are typically related to the tumor pressing on nearby organs or structures. For example, IMT in the lungs might cause coughing, chest pain, difficulty breathing, or symptoms that mimic respiratory infections or asthma.^[15] A tumor in the abdomen might create abdominal pain, a palpable mass that can be felt during physical examination, or digestive problems.

Some patients experience what are called constitutional symptoms, which are general signs that something is wrong in the body. These can include fever, night sweats, unexplained weight loss, fatigue, and a general feeling of being unwell or malaise.^[3][12] These symptoms occur because the inflammatory cells within the tumor release chemical signals that affect the entire body.

Pain at the site of the tumor is another common complaint. One documented case involved severe chest pain that was so intense that regular pain medications were ineffective, and stronger opioid medications were needed for relief.^[9] The severity of pain often depends on whether the tumor is invading into surrounding tissues or pressing against sensitive structures.

In some cases, IMT can cause specific laboratory abnormalities. Blood tests might show elevated white blood cell counts, increased platelet counts, or elevated levels of certain proteins. Some patients have increased levels of inflammatory markers like interleukin-6 (IL-6), a chemical messenger involved in inflammation.^[9] However, these findings are not specific to IMT and can occur in many other conditions.

Can Inflammatory Myofibroblastic Tumor Be Prevented?

Unfortunately, there are currently no known methods to prevent inflammatory myofibroblastic tumor. Because the condition develops from random genetic changes within cells and does not appear to be caused by lifestyle factors, environmental exposures, or infectious agents that could be avoided, prevention strategies have not been identified.

Unlike some cancers where screening programs exist for early detection (such as mammography for breast cancer or colonoscopy for colon cancer), there are no screening tests recommended for IMT. The rarity of the condition makes widespread screening impractical and unnecessary for the general population.

However, once IMT has been diagnosed and treated, close follow-up with healthcare providers is important. Because IMT can recur even after complete surgical removal, patients who have had this tumor need regular monitoring. This typically involves periodic imaging tests to check whether the tumor has returned, though the exact schedule depends on individual circumstances and the tumor’s original location and characteristics.

How Does Inflammatory Myofibroblastic Tumor Develop in the Body?

Understanding what happens inside the body when IMT develops requires looking at changes that occur at the cellular and molecular levels. These changes explain why the tumor forms and how it differs from normal tissue.

Normal myofibroblasts are cells that help maintain the structure of organs and play important roles in wound healing. They share characteristics of both fibroblasts (cells that produce connective tissue) and smooth muscle cells. When IMT develops, these cells begin multiplying in an uncontrolled fashion, forming a mass of abnormal tissue.^[1]

What makes IMT distinctive is the heavy presence of inflammatory cells mixed throughout the tumor. Under the microscope, pathologists see not only the proliferating myofibroblasts but also large numbers of plasma cells, lymphocytes, and eosinophils—all types of immune cells normally associated with fighting infections or allergic reactions.^[1] This inflammatory infiltrate gives the tumor its name and its confusing appearance.

At the molecular level, the genetic fusions mentioned earlier create abnormal proteins that send constant growth signals to cells. The ALK fusion proteins, for instance, act like a switch that is always turned “on,” telling cells to divide continuously. These proteins also activate various cellular pathways that promote cell survival and prevent normal cell death, allowing tumor cells to accumulate over time.^[2]

The physical characteristics of IMT also reflect these underlying processes. The tumor typically appears as a well-defined, lobulated mass. When examined with contrast-enhanced CT scans, the enhancement pattern can be heterogeneous, meaning some areas take up the contrast material differently than others. On MRI, IMT may appear with intensity similar to skeletal muscle.^[10]

IMT generally grows locally, meaning it expands in the area where it originates and may invade into adjacent structures. This local invasion can cause many of the symptoms patients experience. However, unlike aggressive cancers that readily spread through the bloodstream or lymphatic system, IMT rarely metastasizes to distant organs. When distant spread does occur, which is uncommon, it has been documented more often in cases where the tumor cells do not have ALK rearrangements.^[8]

The recurrence rate of IMT varies but is approximately 25% overall, with higher rates in certain locations and circumstances. Tumors that cannot be completely removed surgically are more likely to return. The biology of recurrent tumors may differ from the original growth, sometimes showing more aggressive features or different genetic profiles, which can complicate treatment decisions.^[8]