The expression of CD23 in cutaneous non‐lymphoid neoplasms

BACKGROUND: Cluster designation 23 (CD23) is generally used as a lymphoid marker. Its utility in cutaneous epithelial tumors has never been studied. In our routine practice, we observed that CD23 reacted strongly with eccrine and apocrine secretory coils. METHODS: Immunohistochemical staining of CD23 was performed in a total of 131 cases of apocrine, eccrine, follicular and other cutaneous non-lymphoid tumors. RESULTS: CD23 expression was detected in all benign apocrine tumors and in half of benign eccrine tumors, particularly those derived from secretory coils. CD23 staining was seen in 42% (8/19) of microcystic adnexal carcinoma (MAC), while no staining was observed in tumor cells of desmoplastic trichoepithelioma, morpheaform basal cell carcinoma and syringoma. All mammary and extramammary Paget's disease were labeled with CD23. In comparison, pagetoid Bowen's disease, melanoma in situ and sebaceous carcinoma exhibited negative staining. In addition, CD23 reacted diffusely with cutaneous mucinous eccrine carcinoma in a manner similar to breast or colonic adenocarcinoma. CONCLUSION: CD23 appears to be a reliable immunohistochemical marker of the eccrine/apocrine secretory coil and helpful in identifying sweat gland tumors of such origin. It is of ancillary value in differentiating MAC from its mimicker. CD23 is a useful addition to the diagnostic immunohistochemical panels for Paget's disease.