This article will help you read and understand your pathology report for pleomorphic lipoma.
by Bibianna Purgina, MD FRCPC, updated December 31, 2020
The human body is made up of many different types of tissue. Fat is a special type of tissue that is found throughout the body. Fat is made up of large cells called adipocytes that look clear when viewed through a microscope.
Pleomorphic lipomas are non-cancerous tumours made up of fat and spindle cells. Another name for this tumour is spindle cell lipoma.
Pleomorphic lipomas commonly grow around the upper back and neck but can start almost anywhere in the body. Most grow just under our skin where they feel like a soft lump.
The tumour is usually surrounded by a thin layer of tissue called a capsule, which keeps the tumour separated from the surrounding tissues. The capsule also makes these tumours relatively easy for your surgeon to remove.
The diagnosis of a pleomorphic lipoma may be made after a small sample of tissue is removed in a procedure called a biopsy. Surgery can then be performed to remove the entire tumour.
This is the size of the tumour measured in centimetres. Tumour size will only be described in your report after the entire tumour has been removed. The tumour is usually measured in three dimensions but only the largest dimension is described in your report. For example, if the tumour measures 4.0 cm by 2.0 cm by 1.5 cm, your report will describe the tumour as being 4.0 cm.
MDM2 is a gene that promotes cell division (the creation of new cells). Normal cells and those in lipomas have two copies of the MDM2 gene. In contrast, some cancers that look like lipomas have more than two copies of the MDM2 gene.
Two types of cancer that can look like a lipoma but have more than two copies of the MDM2 gene are well-differentiated liposarcoma and dedifferentiated liposarcoma. An increased number of genes (more than two) is called amplification.
Your pathologist may order a test to see how many copies of MDM2 are present in your tumour. A test called florescence in situ hybridization (FISH) is commonly used to count the number of MDM2 genes in a cell.
A normal copy number confirms that the tumour is a non-cancerous lipoma.