by Jason Wasserman MD PhD FRCPC
September 2, 2023
What is a perivascular epithelioid cell tumour?
Perivascular epithelioid cell tumour (commonly referred to as a PEComa) is a relatively uncommon type of tumour made up of cells that are normally found on the outside of blood vessels. Another name for perivascular epithelioid cell tumour is angiomyolipoma (AML).
Where in the body are perivascular epithelioid cell tumours found?
Perivascular epithelioid cell tumours can be found almost anywhere in the body. However, they are most commonly found in the kidney, uterus, and deep soft tissue.
What are the symptoms of a perivascular epithelioid cell tumour?
The symptoms of a perivascular epithelioid cell tumour depend on the location of the tumour. However, regardless of location, most tumours present as a slow-growing painless mass. For many patients, the tumour is only found when imaging such as an MRI or CT scan is performed for another reason.
What causes a perivascular epithelioid cell tumour?
Most perivascular epithelioid cell tumours are sporadic which means they occur in a person without any known genetic abnormalities. What causes these sporadic tumours to develop is currently unknown. About 10% of all perivascular epithelioid tumours occur in people with the genetic syndrome tuberous sclerosis.
What genetic alterations are found in perivascular epithelioid cell tumours?
Most sporadic and all tuberous sclerosis-associated perivascular epithelioid cell tumours contain a genetic alteration involving the gene TSC2. A small number of sporadic tumours without an alteration in TSC2 will contain a genetic alteration involving the gene TFE3.
Is a perivascular epithelioid cell tumour benign or malignant?
Most perivascular epithelioid cell tumours behave like benign (noncancerous) tumours. These tumours are unlikely to grow back after being removed and cells from the tumour will not spread to other parts of the body. However, a small number of perivascular epithelioid tumours will behave more like a malignant (cancerous) tumour over time. In particular, these malignant perivascular epithelioid cell tumours can metastasize (spread) to other parts of the body including lymph nodes, the lungs, and the liver.
How is the diagnosis of perivascular epithelioid cell tumour made?
The diagnosis of perivascular epithelioid cell tumour can only be made after some or all of the tumour is removed and the tissue examined under a microscope by a pathologist.
What does a perivascular epithelioid cell tumour look like under a microscope?
Most perivascular epithelioid cell tumours are made up of groups of pink or clear-looking round cells. The cells in this tumour are called epithelioid because they look like the epithelial cells normally found on the inside or outside surface of an organ. However, they are not true epithelial cells (in pathology, the ending “oid” is often used to mean “like” or “similar”). The groups of tumour cells are often surrounded by thin-walled blood vessels called capillaries. Mitotic figures (cells dividing to create new cells) and necrosis (dead or dying tumour cells) are rare in most perivascular epithelioid cell tumours.
What other tests may be performed to confirm the diagnosis?
Your pathologist will likely perform a test called immunohistochemistry (IHC) to confirm the diagnosis of a perivascular epithelioid cell tumour. This test allows the pathologist to determine the type of cells in the tumour and to differentiate the tumour from others that can look similar under the microscope. When IHC is performed, the tumour cells will be positive for melanocytic markers (proteins normally expressed by specialized cells called melanocytes) such as Melan-A, HMB-45, and MITF and muscle markers such as smooth muscle actin (SMA), desmin, and h-caldesmon. Tumours that contain a genetic alteration involving the TFE3 gene will also be positive for the TFE3 protein.
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