Inflammatory myofibroblastic tumour (IMT)

By Jason Wasserman MD PhD FRCPC
September 16, 2023

What is an inflammatory myofibroblastic tumour?

Inflammatory myofibroblastic tumour (IMT) is a rare type of tumour that typically behaves in a noncancerous manner. It can be found anywhere in the body including the abdomen, pelvis, urinary tract, digestive tract, female reproductive organs, head and neck, and lungs.

Is inflammatory myofibroblastic tumour benign or malignant?

Although most IMTs will behave in a benign (noncancerous) manner over time, in rare cases, tumour cells will metastasize (spread) to other parts of the body. In addition, IMTs frequently grow into surrounding organs and recur (regrow) after being surgically removed. For this reason, many pathologists classify IMT as a tumour of uncertain malignant potential.

What causes an inflammatory myofibroblastic tumour?

What causes IMT is currently unknown.

What are the symptoms of an inflammatory myofibroblastic tumour?

The symptoms of IMT depend on the location of the tumour. Tumours in the abdomen and digestive tract may cause symptoms related to obstruction including nausea, vomiting, bloating, and abdominal pain. Tumours in the lungs may cause shortness of breath and coughing. Some patients with an IMT have more generalized symptoms such as fever, weight loss, and fatigue.

How is this diagnosis made?

The diagnosis of IMT can only be made after tissue from the tumour is examined under a microscope by a pathologist. The tissue can be a small sample such as a biopsy or the entire tumour.

What does an inflammatory myofibroblastic tumour look like under the microscope?

When examined under the microscope, IMT is made up of spindle-shaped myofibroblasts and fibroblasts. The tumour cells are often arranged in long chains described as fascicles or a fascicular pattern of growth. The connective tissue or stroma surrounding the tumour cells may be described as myxoid, edematous, or fibrotic. Inflammatory cells including plasma cells, eosinophils, and lymphocytes are often seen in the tissue surrounding the tumour cells. The tumour cells in IMT may extend or grow into surrounding normal tissues such as skeletal muscle and adipose tissue (fat).

inflammatory myofibroblastic tumour
Inflammatory myofibroblastic tumour. This picture shows a tumour made up of long thin spindle cells surrounded by light blue myxoid connective tissue.

What other tests may be performed to confirm the diagnosis?

Pathologists often perform a test called immunohistochemistry (IHC) to confirm the diagnosis and to exclude other conditions that can look very similar to IMT. Immunohistochemistry allows pathologists to determine the types of cells inside a tumour by the proteins they produce. These proteins are often called markers and different types of cells produce different markers.

The tumour cells in IMT are usually positive or reactive for the following markers:

  • Smooth muscle antigen (SMA)
  • Muscle-specific antigen (MSA)
  • Desmin
  • Calponin
  • ALK protein (50 to 60% of cases)

The tumour cells in IMT are sometimes positive or reactive for the following markers:

Expression of ALK protein in inflammatory myofibroblastic tumour
Expression of ALK protein in IMT. The tumour cells producing ALK protein are brown in this picture.
Visit the Atlas of Pathology to see more pictures of inflammatory myofibroblastic tumour
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