Grossly, CAF tumors appear as well-circumscribed, firm to rubbery, white/tan to grayish masses some of which appear to consist of multiple lobules. Rarely, these tumors had infiltrated into adjacent muscles or other nearby tissues. As determined by microscopic analyses, CAF tumors are composed of bland spindle-shaped cells in an edematous to fibrous stromal background containing bundles of collagen fibers, small to medium-sized, thick-walled, prominently hyalinized (i.e. glassy appearing) blood vessels, and a minor component of adipose tissue (i.e. fat tissue). Numerous mast cells, moderate numbers of lymphocytes, and small numbers of neutrophils are scattered throughout this stroma; this stroma does not contain the multinucleated giant cells or epithelioid cells that are often found in certain other types of mesenchymal tumors. However, CAF lesions may contain scattered, abnormally-shaped cells, lipoblasts (i.e. immature fat cells), and diffuse malignant-appearing sarcoma-like changes but these findings do not alter the prognosis of CAF as being a purely benign tumor. Immunohistochemical analyses find that the cells in CAF tumors express the CD34 protein in ~50% of cases, a smooth muscle actin protein in occasional cases, MUC1 (also termed EMA) and desmin proteins in a minority of cases, but do not express S100 or cytokeratin proteins. Most cases of CAF in females contain CAF tumor cells which express estrogen and progesterone receptors while limited studies in males reported that 3 of 3 CAF cases contained estrogen receptor-expressing tumor cells while only 1 of 3 cases contained progesterone receptor-expressing tumor cells. Detection of one or more of these protein expression patterns can help differentiate CAF from other types of mesenchymal tumors.
Cellular angiofibroma
Angiofibroma
Fibroma
Collagenous fibroma
Juvenile hyaline fibromatosis
Littoral cell angioma
Sclerotic fibroma
Angiokeratoma