Factor XIIIa is a blood proenzyme that catalyzes intermolecular cross-linking of fibrinogen and is involved in clotting cascade. It has been identified in various tissues including placenta,uterus,and prostate. Anti- Factor XIIIa has been found to be useful in differentiating between dermatofibroma (90% positive) and desmoplastic malignant melanoma (negative). Factor XIIIa positivity is also seen in capillary hemagioblastoma,hemangioendothelioma,hemangiopericytoma,xanthogranuloma,xanthoma,hepatocellular carcinoma,glomus tumor ,and meningioma.