Factor XIIIa (AC-1A1)

 Factor XIIIa has been identified in platelets, megakaryocytes, and fibroblast-like mesenchymal or histiocytic cells in the placenta, uterus, and prostate, monocytes and macrophages and dermal dendritic cells. Anti-factor XIIIa has been found to be useful in differentiating between dermatofibroma (almost all cases +), dermatofibrosarcoma protuberans (-/+) and desmoplastic malignant melanoma (-).1-2 Anti-factor XIIIa positivity is also seen in capillary hemagioblastoma, hemangioendothelioma, hemangiopericytoma, xanthogranuloma, xanthoma, hepatocellular carcinoma, glomus tumor, and meningioma.3