The specificity of this monoclonal antibody to its intended target was validated by HuProtTM Array, containing more than 19,000, full-length human proteins. It recognizes a protein of 83kDa, which is identified as Factor XIIIa. It 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 are positive), dermatofibrosarcoma protuberans (-/+) and desmoplastic malignant melanoma (-). Anti-factor XIIIa positivity is also seen in capillary hemagioblastoma, hemangioendothelioma, hemangiopericytoma, xanthogranuloma, xanthoma, hepatocellular carcinoma, glomus tumor, and meningioma.