Use of classic and novel immunohistochemical markers in the diagnosis of cutaneous myeloid sarcoma.

Cutaneous myeloid sarcoma is often challenging to diagnose based solely upon histopathological features. Although immunohistochemistry can aid in its diagnosis, specific markers have not been clearly identified. We evaluated the utility of immunohistochemical markers in 57 cutaneous myeloid sarcoma cases. In addition to classical markers (CD117, CD163, CD34, myeloperoxidase and lysozyme), we used CD33 and CD14, recently described markers in paraffin-embedded tissue samples, and Kruppel-like factor 4 (KLF-4), a novel monocytic marker. Our results show that lysozyme was expressed in 91%, CD33 in 60%, myeloperoxidase in 54%, CD34 in 39% and CD117 in 36% of cases. An antibody panel that included lysozyme, CD117 and CD33 identified all cases. The monocytic markers CD14, KLF-4 and CD163 were expressed in 60, 58 and 40% of all cases, respectively. CD14 and KLF-4 expression was significantly more common in cases with monocytic differentiation. CD14 is the single most sensitive and specific marker for monocytic differentiation (79 and 80%). Although KLF-4 in isolation is relatively insensitive (50 and 87%), it enhances sensitivity in detecting monocytic cutaneous myeloid sarcoma when combined with CD14. Our results indicate that in addition to classical immunohistochemical markers, targeted use of newer antibodies, including CD33, CD14 and KLF-4 is useful in the diagnosis of cutaneous myeloid sarcoma and in the detection of monocytic differentiation.