Spindle cells are cells that are longer than they are wide. There are many types of normal spindle cells. Tumours, both non-cancerous and cancerous, can also be made up of spindle cells.
The most common type of normal spindle cell is called a fibroblast. Fibroblasts are support cells that are found in a type of connective tissue called stroma.
Some tumours are made up almost entirely of spindle cells. Most cancers made up of spindle cells are called sarcomas although some other types of cancers, in particular sarcomatoid carcinoma, can also be made up of spindle cells.
Your pathology report may describe a non-cancerous (benign) tumour that is made up almost entirely of spindle cells simply as a spindle cell tumour. This is usually an initial diagnosis that will be changed once more information is available. Pathologists often use additional tests such as immunohistochemistry to help them reach a more complete and final diagnosis.
Similarly, a cancerous (malignant) tumour may be called a malignant spindle cell neoplasm until a more complete diagnosis can be reached with the help of additional tests or additional tissue to examine.