This article was last reviewed and updated on July 14, 2018.
by Bibianna Purgina, MD FRCPC
Pleomorphic lipoma is a non-cancerous tumour made up of fat and long thin cells called spindle cells.
Most tumours start around the upper back or neck.
The tumour usually feels like a soft lump just under the skin.
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 most commonly occur around the upper back and neck but can occur anywhere. Most pleomorphic lipomas occur just under our skin where they feel like a soft lump.
Most pleomorphic lipomas are 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.
Another name for a pleomorphic lipoma is a spindle cell lipoma.
These tumours are measured in three dimensions but only the largest dimension is typically included in the report. For example, if the tumour measures 5.0 cm by 3.2 cm by 1.1 cm, the report may describe the tumour size as 5.0 cm in greatest dimension.
Tumour size will only be described in your report after the entire tumour has been removed.
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 (malignant tumours) 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 (benign) lipoma.