These cancers form from the fibroblasts (cells that produce fibrous tissue) and other supporting tissues, most commonly arising beneath the skin.
They commonly present as gradually enlarging firm masses under the skin. The degree of malignancy of these tumours varies – some are highly malignant with extensive local invasion of tissues, and early metastases occurring to lymph nodes and the lungs. Others are less aggressive and will not be so invasive or metastasise so readily.
The most common sign in a cat with a fibrosarcoma is a progressively enlarging firm swelling under the skin, but this can affect almost any site.
Optimum treatment usually involves a combination of surgery with radiation therapy and/or chemotherapy, although the prognosis is variable depending on how aggressive (malignant) the tumour is. For small tumours that have not spread, surgery alone may be curative.