Desmin is a protein made by muscle cells. It is produced by both normal muscle cells and tumours made out of muscle.
There are three different kinds of muscle cells in our body:
All three types of muscle cells produce desmin. Tumours made up of muscle cells also produce desmin. These kinds of tumours can be non-cancerous (benign) or cancerous (malignant). Most cancers made from muscle cells are called sarcomas.
Desmin can also be produced by a cell that was not originally a muscle cell but has started to look and behave like a muscle cell. In this case the cell will usually also produce proteins that not normally made by muscle cells.
Pathologists perform a test called immunohistochemistry to look for cells producing desmin. This test helps your pathologist decide if the tumour is made up of muscle cells or if the cells are starting to behave like muscle cells.
If the cells in your sample produce desmin, your pathology report will describe the cells as positive or reactive. If they do not produce desmin, your report will describe the cells as negative or non-reactive.